I have an older Trek 800, complete with Biopace chainwheel. Today I noticed for the first time that there is intermittent clicking emanating from the general area of my crank. The clicking is loud enough to cause vibration throughout the frame, which make me think it is not the pedals. The pedals look pretty secure on the crankarms anyway. I checked the base of the crankarms to see if there was any gunk that might be causing it, but I didn't see anything.

The weird thing is I can't seem to reliably reproduce it on any given pedal stroke, but it is something that I will hear multiple times in a 30 second period. Earlier, I looked at that part of the frame for cracks, and didn't see any, but just in case, I wanted to check it out. I am wondering if this might be a problem with the bottom bracket...

Your advice would be most welcome.