Loud knocking during printing. Suspected Z axis but dunno anymore

If anyone else is having this issue please do post. We would like to know how many are out there

The reson ? - Bambu Support is not really impressing me and I feel there needs to be some pressure put on them.

My ticket number is US260601389001. Raise a ticket with them. Describe your problem - mention that this happnes with new firmware and everything is fine with the old firmware, mention my ticket number to make them link all of these cases together (there are currently two of us that are in touch over Reddit that have done this and Bambu Support confirmed to both of us that our cases were linked).

And lets put pressure to have them do something about this. The GCode they sent me under the premise “please run this and confirm if the kocking is gone”, which means they were fully expecting this would fix it - it did absolutley nothing.

I am a bit pissed to be honest and doubdting how seriously they are treating this.

Check the top of the rear z axis screw. The two front z axis screws sit in a rubber cup at the top, but the rear screw does not have this rubber cup. Maybe the rear z axis screw is tapping the metal at the top.

Here’s my extra two worthless cents about all this.

The new noise cancellation algorithm is working on a vast majority of printers without a problem. I believe H2D’s (and H2S?) have had it for a while now and they all use the same XYZ motion system. So it would be logical to assume H2C would work exactly the same, right ?

Well, I have had the unfortunate pleasure to go through several H2C units, which were returned due to various defects with them. This took place over several months, since launch. I did have a launch unit.

From that experience I have learned that even in the span of 3-4 months, the units I was receiving have had part variations in them, for the worse.

The launch unit developed a fault with XY motors. Its replacement did also, but that one also came with extremely noisy exhaust fan. I had both units for a short duration together and was able to take the fans out to inspect – they were completely different ! With the newer unit being so bad it was shocking. I kept the original fan moving forward, and several printer replacements later, that same original fan is still with me as every single one after the launch unit came with the new, horrible one.

I already mentioned that I received a replacement Z motor for this current one, which is also completely different from the stock one, having both visual physical differences, but more importantly – mechanical/electrical ones as well as it runs smoother and quieter. This kind of variation is not acceptable to me! I hate that Bambu is doing it. It is NOT like-for-like. The exhaust fan is absurdly worse than the original unit I cling on to. The Z motor is audibly inferior as well. I am scared to think just how many other, far less noticeable components are exposed to this kind of “variations”.

I know manufacturers source components from multiple sources, that’s how mass manufacturing works, but more often than not, new sources are introduced due to costs cutting measures.This approach does not always produce a like-for-like component. Exhaust fan and Z motor are two examples of that, I am sure if I had more components to replace, I would notice more of that.

Personally – I am convinced this is what is happening here with the knocking again, an alternative component (that is obviously saving Bambu money) started making its way into newer units, and it turns out - is not behaving the same as the original and Bambu now needs to scramble to try to work it out as – even if they noticed an issue and corrected it by going back to original part - until all of those affected units trickle out of the supply chain, this is what a lot of users will get. And I bet recall is not a financially viable option.

They could simply identify the offending part, and send out replacements though. However, what I really hate about this situation is that they are not admitting or revealing which part is at fault. Which, to me, means they prefer to hide it and try to mask with firmware they are supposedly working on.

What concerns me is that they offered me to replace this printer quite early on, at the same time saying that the replacement “may” also end up having the same problem. Which could mean this potential new component made its way to a lot of new units already and its just a matter of time more and more users start noticing the issue.

Then again, if new unit is sold and from the start is used with new firmware, the user might not even know the printer should not be doing this knocking and would assume this is just how it works. Perhaps this is part of their strategy ? Then again, it cant be, as there already are the likes of us, which will hold Bambu accountable and will not accept anything less than a full resolution to this.

Don’t really know what to say. The fact they are both keeping quiet about this and are extremely slow with replying to me, making little to no progress in fixing it, does give me reasons for concern.

Their very first response I received when I reported this problem was, and I quote: “rest assured that the sound you have noticed falls within the normal operating range of the printer, so there is no need for concern in this regard”. Which, pardon for my French, effin sent me ballistic.

Their first attempt at fixing it did nothing (gcode). It sure feels like they didn’t even bother to get a unit with the same exact issue, replicate the problem in the lab, and work on a reliable fix there and provide one ASAP.

Instead, it feels like they are making very relaxed “stab-in-the-dark”, “try-this” attempts, using our printers to test if it has worked or not.

If this is how they are going to be developing a fix for this, it will take years of back and forth.

I am sure I have made a ton of logical errors and/or I am simply wrong about a lot of what I wrote. I accept it and apologise if anyone is offended by my stupidity. I just wanted to vent a little as it has been well over a month and Bambu seems very relaxed about this and is yet to provide a fix.

Hi MiamiJerry,

Thank you for the advise, however, as confirmed by multiple users, including myself, doing several back and forth downgrading and upgrading - loading old firmware immediatelly resolves the problem, loading the latetst one back in, brings the knocking back.

Its not mechanical it seems.

If the noise is the rear z axis screw at the top, then the noise should go away if you install this STL;

https://makerworld.com/en/models/1373683-h2-series-rear-lead-screw-centering?from=search#profileId-1420835

I don’t recommend this as a long term fix….

its from the bottom if anything, and actually from the Z motor.

Hi, I don’t know if you’ve already tried this (I admit I haven’t read the whole thread very thoroughly), but try changing the “Z-hop type” in the Slicer to **normal**. Then try reprinting the same .3MF file that’s giving you the problem and see what happens. It worked for me and my H2S.

Thanks, I will.

However even before trying - if I am not mistaken, the Z Hop type dictates what XY axis does during hops.

Our issue is actually with the Z axis and bed movement, when it changes direction rapidly, like during a Z hop, it generates a ■■■■, like demonstrated in this video.

At this point we are trying anything and everything, but considering Bambu has confirmed this to be an issue, and are working on a fix, I doubdt its going to be as simple as changing a setting.

Especially considering there is absolutley no issue when rolling back the firmwere to previous one. This is to do with the new noise compensation alogrithm. Clearly some printers do not behave as expected …

Please try it, and then let us know if it helped. ** Z-hop ** determines how the nozzle tip “moves” away from the printed part. If set to ** spiral **, a combination of movement with the X, Y, and Z axes occurs; if set to ** normal **, only the “downward” movement of the Z axis occurs. it worked for me. I can’t explain why…but it worked and is working on my H2S

If the top of he rear z screw is near metal, firmware may just be not slapping it as hard against the metal. Don’t discard simple thing in your search.

understood. thank you.

Will give that a go as well.

Jesus, it indeed fixes the knocking ! The ■■■■ ???

Does that mean you also had the knocking issue or did you change the Z Hop type for a different reason ?

Hi, I’m glad you tried, and I’m glad your problem was solved.
I always printed very well as long as I was using the firmware 01.01.02.00, but then I started having the “metallic clacking” problem when moving the Z-hop as soon as I installed the various beta versions of the firmware up to the latest version 01.02.00.00. Like you, I also noticed that by reverting to version 01.01.02.00 the problem disappeared. At that point, I started experimenting with the Z-hop until I found this solution.

Thank you for your help.

It makes no sense though. How is this not a big thing with community in uproar screaming for a fix. Why aren’t more people talking about it?

Did you report it to Bambu? Are they aware there was a bug in beta which is still present ?

How in the world did this find its way into final release ?

This is pure madness.

Yes, Bambulab’s customer service team is aware of the problem, as I, like you, have opened a ticket. I don’t want to play devil’s advocate, but I think Bambulab has too many irons in the fire, and this leads to long waits and a bit of confusion. Even though I only print as a hobby, I’m very happy with my H2S, but this is the reality. Bambulab’s customer service team does its part, and I thank them, even if sometimes it’s not enough.

I hope that in the next firmware version this suggestion of mine will be taken into consideration, so as to definitively resolve this problem.

Thank you for your resposne.

I applaud your composure and professionalism.

May I please ask since when was this going on - as in when did you got in touch with Bambu?

I am very surprised. From the way Bambu has been responding to me it never occured to me they are in the slightest aware this is this well known issue.

To the contrary - it seemed to me as if what I reported is new to them, cosindering that after a month of wait they sent me this gcode with ran z axis caliblration with some additional undocumented parameters, asking me if this resolved my problem …

Thanks for your comment. I’m very happy to have been able to help a professional, because as I said before, I only print as a hobby. To answer your question, I opened a ticket with Bambulab support on April 5, 2026.

oh dear. So they knew about the problem while it was still in Beta.

Then they decided to ignore it and released the public FW anyway, with this issue in it.

Since release of public FW more users are popping up questioning what is happening, and the Support Team (and RnD Team) are not even briefed to know about this, direct this to the correct team who (hopefully) is working on it, and provide accurate information to the user …

This is terrible…

codsidering it has now been 3 months since they knew about it, my guess is this is not getting fixed.

I will entertain a probability of the next FW release fixing it, but i sense a printer replacement is in order for everyone affected.

3 months. What is Bambu thinking ?

This is not funny.

I also hope that the next firmware release will definitively fix the problem. I’m currently using a beta version of the firmware with the Z-Hop parameter set to normal… and I’m not even considering changing this balance…

why are you on a beta version ? Isnt public the latest with no new betas available at this point ?