I was doing what started out as a 35c pitch raise today on a 1969 S&S console. Room was 71F and 15%RH. Musical, elderly owners.  About in octave 5, I heard a kinda thunk noise that sounded like it came from below. Removed knee board, looked around, saw nothing amiss near as I could tell.  Then noticed the crack between the pinblock and back at the far bass end. At the time, I wasn't in the habit of checking for such things prior to starting a tuning (my really bad bad) so I'm not certain whether it was there before. (Yes, I'll be checking that before EVERY tuning from here on out!) Decided to press on. Discovered that the notes I'd just tuned were very flat, and the 35c I'd been pitch raising now was more like 80c.  As I completed my PR pass the top 6 or 8 notes were close and required very little overpull. The low bass was also still close, but flat. Could this fairly short and narrow (about 12" x < 1/16 at widest point) separation have that dramatic an effect? The separation did not change from the time I first noticed it until I left after speaking to the owners (at least 1/2 hour.)  Could the thunk noise have been something else that would cause this? I think cracked plate, but from all the reports I've read here that is more like a shotgun blast. This thunk was like dropping a 4" piece of 2x4 onto the bottom board. Thanks, Paul Bruesch Stillwater, MN