The disc motor has a loud sound (haven't noticed it earlier).
I have tried Stern Service Bulletin #169 (applied a few drops of machine oil at the top and bottom of the motor shaft). This bulletin is really for Pirates... but can also be used on Tron.
The oil did not help. Check out the two videos below. The sound is louder when the motor is in place. First I thought that the disc touches the sides but that is not the case.
What could be wrong?