RE:
While I will need to run a few more test parts, I replaced the smooth idlers on the X and Y axis with genuine Gates 2GT toothed idlers and it seems to have almost completely eliminated the VFA along my Y axis.
After I run a few more sample prints, I will post back here with a list of all of the things I originally tried that didn't work. If for no other reason, it can give someone (or future us) a list of things to try when improving print quality.
If anyone else wants to try the same modification, I have uploaded a new model to Printables to accommodate the wider idlers (Prusa smooth idlers are 9mm wide whereas the genuine Gates 2GT toothed idlers are 10mm wide). Give it a try: https://www.printables.com/model/629728-mk4-idler-ends-for-toothed-idlers
Please note, you will definitely need to re-tension your belts after switching idlers since the radius around which the belt travels will have changed.
RE: Heavy VFA on a "no VFA" printer
Thanks Justin for sharing! I will give it a try. I just have to find them in some store in Europe.
RE: Heavy VFA on a "no VFA" printer
So I had this issue on one of our MK4s as well and I think I mostly fixed it.
You have to loosen your belts (in my case only the Y axis had this weird belt ringing), don't tighten your belts more because this will make the issue even worse
RE: Heavy VFA on a "no VFA" printer
Had a similar issue. First 2 with the smooth Y idler. Second 2 with generic toothed idler. Helped a lot for my issue.
RE: Heavy VFA on a "no VFA" printer
While I'm happy you're getting your belt ripple issues fixed, these are NOT VFA. I had these issues as well once and they were fixed by replacing the pulley on the affected axis.
But VFA are something completely different, a lot more fine, thin, with very little space between the artefacts. And in case of MK4, not on pure X nor Y movements, only at angles. VFA are caused by motor resonance.
I don't want to be rude, but you're kind of overtaking a VFA-focused thread with a different issue.