I have a bit of a puzzle here.

Bought an M645J from an online auction. Everything seems pretty good--shutter fires accurately (as far as I can tell), installed a new battery that works fine, focus on the standard 80mm 2.8 moves smoothly, NM prism is clear.

Only trouble I'm having is that the mirror lift makes a squeak/chirp about 50% of the time on all shutter speeds. Sound of the shutter itself is clean.

The weirdest part: If I hold the camera upside down the sound goes away every shot.

I think that the light seals are rotting out--I get some black dust here and there--and I wouldn't mind buying a kit and replacing them (along with the mirror bumper) but if this is unlikely to fix the problem, I think I'd rather return the camera and keep looking.

What do you guys think?