So long story short my buddy got scammed on a mini Revo so I've been slowly replacing all the torn up and worn out parts on it. One of the last things left is the motor. I noticed when you turn the pinion on the motor, every revolution it 'clicks'. My personal mini Revo doesn't do this. Motor is butter smooth when you turn it. I imagine something is broken inside his motor? It runs but it sounds hurt when it does.
Figures. This thing has been a money pit trying to make it right again.