I thought I discerned a slight thunk emanating from inside my newly acquired Seamaster chronograph when I was changing the incorrect bracelet. It was a pretty subtle sensation at first, but recently I've felt it so clearly that I got spooked and decided not to wear it until I could investigate it properly. It may just be a Telltale Heart thing with my guilty conscience. Nothing I that I can see appears to be missing or loose, but then again I have no idea what I'm talking about. Am I missing something obvious?
Is there something holding the movement in? Not an expert on those but on other 321 and 861 models, the dust cover under the caseback acts to hold the movement in place, there are no case screws. If that is missing you will get a problem.