@feri The noise is for sure related to Z-axis moving. I guess the issues are either the stepper motor or the guide bar. But it sounds more like a mechanical mechanism getting stuck.

If it were me. Step1: I will disassemble two guide bars and only test the Z-axis stepper motor to see if the noise comes from the motor. Step2: I will check if the Z-axis and motor installed correctly/paralleled.

I found that when you up the bed, there is no noise, the noise only comes when Z-axis moving down. The Z-axis is fixed on the motor and there is no fix on the top which means the higher it goes, the more moveable space it has. Therefore, even the Z-axis is not parallel to the two bars, when the bed goes up, there may be no noise, but when the bed moves down...you know.

@kevin Thanks very much for the reply, 

Yes I can confirm that the motor is fine and it is all because of the bed, so basically if I hold my finger under the bed and push upwards a bit the noise goes away. 

But how can I fix it? 

I can't hold my finger under the bed all the time lol

Also how comes it wasn't like this at first and just after a few prints it started happening! 

@feri Reinstall it and rub some petroleum jelly. Let's see what happened next.

Sure will do that, I hope it helps. 

Thanks a lot ?

I have the same darn issue.  WTH???

It makes a squeal/squeak as it's moving down until about 1/4 of the way, then it's quiet.  Moving up is fine.  I've put 3-in-1 oil on the threaded rod and smooth bearing rods, it only helped a little.

The squeal is loud enough that we can't use the phone while it's printing.  BIG problem for the office.

If anybody else figures out what exactly is causing this noise (brass threaded blocks maybe?) please share your solution.

thx

edit:

Figured it out.  It was the brass bushings riding on the threaded rod.  Tried several types & weights of oils, nothing helped until we switched to synthetic grease with PTFE (teflon) in it.

@rc3105 As it sounds like something getting stuck. Have you tested it manually? Disable the stepper, and move the bed manually to see if the same situation exists. If so, you have to check the if Z-axis and the two guide bars straight enough and if you installed them totally paralleled.

Figured it out. 

It was the brass bushings riding on the threaded rod.  Tried several types & weights of oils, nothing helped until we switched to synthetic grease with PTFE (teflon) in it.

@rc3105 Hello, That is great! Would you please share the synthetic grease you used?

Crazy you have to put grease on something you just spent so much money on.