Persistent Y-Axis Rattle on MK3S+  

Persistent Y-Axis Rattle on MK3S+

Hi everyone,

I’m trying to diagnose and resolve a persistent Y-axis rattle on my MK3S+ and would really appreciate some advice and guidance.

The video below demonstrates the rattle at it’s loudest/most consistent – when the Y axis is making rapid changes of direction.

https://www.youtube.com/shorts/nwqnRgaMw9Q

Symptoms

1. Pronounced mechanical rattle/chatter from the Y carriage, perhaps stronger when the bed is in the back half of the carriage.
2. The rattle is extremely pronounced during infill.
3. It does not rattle at all during the movements of mesh bed levelling.
4. The sound is mechanical, not stepper noise etc.
5. Using a mechanic’s stethoscope to check the bearings, rods, motor and mount, belt path and y carriage frame. I’m 95% sure the noise originates from the left Y axis rod or something attached to it.
6. Occurs mainly at slow or medium speeds or during frequent direction changes.
7. Prints have VFAs, but no other quality issues.

Troubleshooting Attempts So Far

1. Cleaned the bearings thoroughly with IPA, repacked them with lithium grease and also tested them separately with Prusa’s supplied lubricant.
2. Replaced all three Y-axis bearings with Misumi bearings taken from another MK3 that runs quietly.
3. Replaced the left Y-rod with a new one.
4. Rotated the rod in the holders to test for straightness/tolerance variation.
5. Loosened the rod holders and applied inward/outward pressure before tightening.

Throughout all of this, I have disassembled and rebuilt the entire Y-axis 5–6 time in total, following Prusa’s online build guide each time and performing the “bed slide alignment” procedure multiple times. Rattle persisted with all bearing sets, lubrication types and other attempts. The Y axis belt tension reads exactly centred in the optimal range using the PrusaMobile App. I haven’t tried DryLin bearings which I’ve avoided so far because many users report tolerance issues. Open to reconsidering if the community believes it’s the right next step.

Result: left Y-rod/bearings are the strongest noise source.

Clues

1. Pressing on the bed reduces the noise
2. If I press upward or downward on a corner of the heatbed during printing, the rattle diminishes noticeably.
3. If I press from inside → outside at the front of the left Y-rod, the noise drops 60-70%. However, despite multiple attempts (loosening, repositioning, tightening), I cannot get the rod holders to stay in the position where the noise disappears.

Links

Some of the forum posts/videos of other users who have experienced the noise and things that I have tried:

1. https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-assembly-and-first-prints-troubleshooting/rattle-noise/?__cf_chl_tk=nxrZ46QaHiztrMzpKFx1I2qxThusCGdfyOT9GmZ41ik-1754555869-1.0.1.1-O63uRSra1JYNln4wjlzqMFy863vzam8_3qwV4.41rYQ
2. https://www.reddit.com/r/prusa3d/comments/lxrmce/prusa_i3_mk3s_bearings_rattling_problem/ https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/y-axis-bed-rattle-when-moving/

Thanks so much to anyone who can offer insight. I will happily try any other corrective measures, or retry any ones I’ve already attempted. I’ve put a huge amount of time into diagnosing this and would love to finally get it fixed. Any help is very much appreciated!