One theory I might put forward is that one of the rod bearings may be defective or the base units may have shifted. Isolating which one can be the challenge.
Check this post regarding remedy for bearing rod popping out of the bottom of the P1 series. This is a quick check and quick fix if that is in fact what is causing this: Solution: The build plate is not placed properly
Here is another version of this problem but elsewhere in the travel path: Loose Bearing - #2 by Olias
It might help you isolate the problem but have you tried to use a sound meter app on your phone then hold the phone near each of the three lead screws and rods, both at the top and and at the bottom. Taking measurements or doing a simple recording and isolating where the sound is loudest might help in identifying the location of the noise. Then you can focus on observing that sections under a bright flashlight and see if you can notice any unusual screw or rod movement.
Here are two examples of apps that I’ve used to diagnose sound issues.
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Alternatively, you can pull a page out of the auto mechanics’ playbook for isolating noises inside an engine compartment. This method of noise isolation works for electronic motors too.
I used this auto mechanics stethoscope to determine the location of a faulty fan in one of my PC builds. With a PC case using five fans, it was very difficult to diagnose which one was causing bearing noise. This device has a contact rod option which allowed me to place the tip of the device right onto every fan housing and immediately hear which fan bearing was causing the noise. It would likely do the same if you placed the tip against each lead screw and bearing rod. You would hear any change in noise very quickly this pinpointing the location of any specific interference. Of course if it is a binding issue that is caused by plate misalignment, the noise may not be isolated but coming from all three locations. That too would be a useful clue.
