Clunk.
Clunk, clunk, clunk.
My printer is in the next room from where I work, and that’s what I heard one day. I watched it for a few minutes, but it didn’t take long for me to realize what was causing the noise. Every time the printer would move in Z it would clunk.
I’ve spent so many hours dialing in my settings, making sure that my table is level, etc but I forgot something important. Lube the Z axis lead screws. Make sure that they are tight in the motors and don’t spin unless the motor is spinning.
Someday, I plan on putting together a maintenance checklist. This will definitely be on it.