I don't have a stethescope so I used a long wooden stick. Seems to be in the bottom of the engine. Dang it.

I just talked to the guy I bought the car from. He said he really, really doesn't think it's a main bearing.

In trying to recreate the sound for him, I tapped two rings (for fingers, guys, ;-) not pistons) together quickly. That's the sound. Doesn't seem to be effected by RPM, either.

I really hate the idea of pulling this engine (I think I may have already mentioned that) so I'm hoping for other less time consuming and expensive things to try before I do that.