Quoted from nibre: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.
Any ideas?
The Stern Service Bulletin worked great for my motor. Since it's not working for you, it's a cheap part to replace (https://www.pinballlife.com/replacement-motor-for-stern-shaker-kits.html).