Thanks for your reply, Elliott.
I have uploaded two new videos, but I didn't manage to do one with the car on the track. The problem started between two heats, and last year's indoor season and this year's outdoor season I had no such problem. My 4th battery of this indoor season, it started with this.
Sorry for the ending of the first video, but the lamp providing light for the video fell down into the car because of the vibrations
The car-stand actually dances around the table because of it
The problem might not be that visible in these videos, because I tried changing motor from 5.5T to 17.5T (but with same gearing at FDR 7.8 and minimal timing) to see if that was the problem, but it wasn't. So the motor can't pull that many RPM's
Normally with wheel chatter you can barely hear it on the track, but this I can very clearly hear. The grinding noices are still there on the track. I tried getting some of the other Tamiya's at the track (both 417's and 416X's) to do the same (steering plus throttle on the carstand) with very little to none vibrations at all, and almost no noices. So I have a feeling this isn't normal wheel chatter.