Extruder Missed Steps (?) Right After Ramming  

Extruder Missed Steps (?) Right After Ramming

Hi all, I recently got my mk4s, original Prusa enclosure, and MMU3, and had a blast putting it all together!  I'm now working on fine-tuning the setup, but I'm running into a minor issue (I think) that I can't seem to resolve.

During color changes, usually right after ramming, the extruder sometimes makes a reasonably loud click sound.  My best guess is that this indicates missed extruder steps (or possibly slight filament grinding?) during the retraction after ramming, but I can't identify for sure the source of the noise or exactly what is occurring when I hear it.  I don't think this is causing print artifacts (though I do sometimes have stray lifted tracks on the wipe tower, not sure if related) - though it doesn't "sound normal", and doesn't consistently occur, so I want to make sure it doesn't indicate an underlying issue or potential longevity problem.

The sound occurs only during color changes, but occurs approximately half the time at each color change.  It occurs both with pre-sliced gcode (e.g. the 5-color test) and self-sliced gcode.  I've attached two videos that include the sound.  (In one of the videos, it sounds like there's two clicks, but the first one is just the nozzle going over a stray lifted track.)

In case the videos don't work, a more detailed description of when the 'click' occurs: The print head finishes one color on the object, then moves to the wipe tower.  It immediately performs some rapid extrusions for a few seconds (ramming, I presume), and the 'click' occurs simultaneously with the end of the last rapid move.  (It never occurs during the moves themselves.)  Then it proceeds with the rest of the color change without issue.

My setup is currently a fairly stock kit-built MK4S+MMU3+Enclosure setup, following the instructions, though the nozzle is an ObXidian nozzle (0.4mm, non-HF) rather than stock brass.  After noticing this sound, I've made the following changes to try to reduce friction in the filament path:

- Replaced the MMU3 mounting feet with this version that mounts it horizontally to the frame, minimizing filament bending when mounted in the enclosure configuration.
- Shortened the PTFE tubes going from the buffer to the MMU3 to a length that minimizes length and bending while still allowing the lid to open.
- Replaced the PTFE tubes going from the spools to the buffer with 3mm ID tubing to minimize friction.

None of these changes appeared to have an appreciable affect on the frequency of the noise occurrence; but they do seem to make filament easier to hand-feed.  I've also attached some pictures of the filament path.

I guess my questions are:

- What might be causing this noise?  Is it likely skipped steps during retraction, or something else?
- Is this even something I should be trying to resolve at all?  (Any chance it could be related to stray lifted tracks on the wipe tower, or could result in a shortened lifespan?)
- Is there anything else I can try to stop the noise from occurring, either in hardware or slicer settings?

Thanks in advance for any help!

Click is audible after ramming.  (First "click" sound is just nozzle scraping stray lifted track.)

Click is audible at very end of video:

Inside enclosure:

Filament path from buffer:

Filament path to MMU: