Mine started at around 200 hrs. Its not nut wear. I followed the Nut Wear thread where you and a few others did a ton of excellent work and immeditelly I thought it was that. First resposne was Bambu sending me screw and nut set but before I put them it, I did a lot of investiagtion into it and found that my nuts are perfect and its actually something else (firmware). I replaced Z motor, did several belt remounts and retensions. tried jerking the Z belt by hand trying to replicate rapid direction changes during operation when the knock happens. Cant do it. I even removed the Z motor, put the belt on and tried the same that way just to check if there is any mechanical issue in the nuts or screws anywere. Nothing.
The knock only happens when the printers is runing on its own, during spiral Z Hop. Normal Z Hop is a lot quieter, (sounds almost as if knock is gone, but its still there, just very faint). I know that Z hops suggest its not JUST the Z axis, but it is. There is a video made by another user where he maxed out ZHop distances to exaggerate it to see when knock occurs. Its exactly at the change of direction of the bed. That video is in somwhere my thread linked below.
Aaaand - old firmware does not do this on the affected printers. There is no play anywhere. No mechanical issue to speak of. Even replacing the Z motor makes no difference. My guess is perhaps the driver board but Bambu is adamant that NO. Saying that best course of action is to wait for firmware update.
Oh, in the meantime they were sending me a few variants of gcode that runs Z noise compensation calibration with extra undocumented parameters. Those made no difference even though Bambu says this fixes things for others. They also confirmed that the fix coming in the firmware release is different to the gcode attempts they were sending me so in guessing even if gcodes did not work, firmware should ?
Having said that, they did offer to replace the printer for me … so I am not all that convinved they beleive they can really fix this. Time will tell. I am giving them the benefit of a doubdt and will wait for the firmware. The moment it out and does not fix it, I am replacing the machine.
There is more on that in my origial thread here
When I noticed it, seems I was alone. Now, especially after 1.04 for H2D, there seems to be a ton new reports of this. I find it baffling as H2D had the new motor noise compensation (and new stepper curves) since 01.03.00.00 (20260303) and from what I understand, the first reports of this stem from that firmware. Then it spread onto H2C with 01.02.00.00 (20260601) which is when I started noticing it. Reverting to 01.01.05.00 (20260211) fixes it completley just like for everyone else affected that I spoken to.
Oh one final thing. Even though I spoken to users who said they had this since April on H2D’s and did raise tickets with bambu, when I raised mine, the front line support had no clue about this being a known thing. I imagine that might still be the case, which is why I am suggesting to everyone to mention my ticket number. It took a while of back and forth and futile tests, tweaks and parts (screws, nuts, z motor), but eventually this has been passed over to their RnD team who were issuing me those gcodes to run and said the firmware will fix it. Hance, when you do raise your ticket, expect complete blank face and totally missing-the-point reply.
But do raise your ticket. Pressure, pressure. pressure. One angry customer is easy to ignore. A whole bunch screaming at them may be a bit harder to.