nasty scratching screeching sound & Extruder steps lost  

nasty scratching screeching sound & Extruder steps lost

Hey there,

my MK3S is making strange sounds. It's really annoying to have the printer running like this in the background.

I think the sound was there quite a time but quieter. It got really loud and annoying while printing the "drum gear" part of this thing: https://www.thingiverse.com/thing:4076827
Because of the teeth of the gear I think its more audible...

I started with the drum gear part and printed the complete thing over the last two days. To get rid of the sound I tightened the idler-door-bondtech-thingy a bit and first it was fine. After ~35-40 hrs of almost constantly printing (there have only been some 5-10 minute breaks and one ~3hrs break while I was asleep) I printed some other gears of that thing and to get the overhangs working without using supports I turned down the layer height (variable layer height is really awesome!!). When the printer got to the 0.07mm layers I heard a "clicking" sound. Obviously the Extruder wasn't feeding PLA any longer. Never had this before, so I was a little bit confused. I paused the print (thanks to octoprint) and heated the nozzle from 211 to 215 and tried to extrude and retract a few times. I tried to continue the print but had to abort it due to a too big gap in it. (was only producing spaghetti...)

So I restarted the part, turned to temp to 215 (I use 215 for first and 211 for following layers to minimize stringing with black PLA from "Das Filament") and thought I'd be good. Cracking / clicking sound again, and again at the same layers. So I paused again - this time I was in time - fiddled around with the extrude / retract in octoprint and it started it extract PLA again, so I just continued successfully.

Because I needed another drum gear in the end I started the same part again, which I had printed first about 35 hrs ago.

Although first time everything went great, this time I had Extruder steps missing again (crack crack crack). So I was wondering again ... and came up to the thought, that I over tightened the idler door. Extruder stepper was almost at 50°C...
So I loosened it up again, no steps missing but the nasty sound is back ... 

Here it is:
Video on Google Photos

It doesn't sound like this:
https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-others-archive/creaking-noise-coming-from-extruder-assembly/
But could it be this?

Or the ptfe tube?
https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/hotend-ptfe-tube-length/

But why is it gone if I tighten the idler door?

Any ideas?

Kind regards

Andreas