Quote Originally Posted by AgX View Post
That special noise seems to come from the mirror damper, thus any problem related to it should not cause exposure error.
Very close but........It's the mirror governor on the side of the mirror box. It's just a series of gears meant to regulate the speed of the mirror's rising.
It's very similar to a slow speed escapement in a leaf shutter where the last gear engages a pallet for consistant speed.