Rivits do loosen and can fail with vibrations. I speak from experience, a loose rivit popped out and almost cut a driveshaft in half on the CH-47D I was flying. Had the drive shaft failed, the tandem rotors would have decoupled and the aircraft would have had a mid-air collision with itself (front rotors contacting rear rotors).

However, a helicopter does vibrate a little more than a chinese 2 stroke engine but only a little more :-)

Thanks for the tips.