Dreaded loud hot bed humming...
I've spent hours researching a way to reduce the dreaded hot bed humming on my MK4. My printer is no exception: on certain speeds, there was a very loud humming noise from the area of the hot bed.
I found there are many things to try/check and none seemed to solve the problem. Finally, I decided to check belt tension. Apparently, the belts have stretched a tad since new so they were both slightly on the "loose" side. I tested this both with the iPhone as well as with the printed belt tension tool.
And... This is what I found when I flipped the printer on it's side:
Here is the belt tensioner - you can see the missing m3 screw...
The right hand side m3 screw on the y-belt tensioner was so loose that when I touched it, it fell out. The screw on the left was also not tight. Both belt blocks were loose enough to rattle. Once I put all this back together and tried a print I knew would cause the printer to hum, I noticed the great majority of the racket is gone. Not 100% - I suppose there are other things causing the hum, but I thought this might help somebody.
RE:
The original belt tensioner (at least of my MK3S) is not great and according to the photos, has not changed substantially with the MK4. You can keep it with the screws secured with something like loctite. Better yet: You can also use an additional y-axis belt tensioner. There are plenty on printables, like this one. Then you can retension it safely and way more comfy. If you like, even while it is printing but that usually is not necessary.
RE: Dreaded loud hot bed humming...
Agree on the tensioner design - there is indeed room for improvement. Also, thank you for the link for the tensioner alternative.
I did a few searches once I got the printer working again, to find alternatives. This will be next on the list of things to print.