Thanks everyone. Sorry for conflating terms, but I'm pretty sure the issue is a wheel out of balance (we use the term "truing the wheel" in cycling to refer to removing the wobble in the rim by tightening the spokes). Anyways, the issue came about as I've become increasingly annoyed by a slight wobble in the blade which, at times, prevents me from getting a straight cut (I don't have a table saw so I rely on the bandsaw for crosscutting). Even when I'm tuning the saw, I notice that the blade will wander from side to side so that getting the guide blocks properly spaced is difficult (I have replaced them with cool blocks). I noticed the problem when I replaced the tires a few months ago and spent quite a while running my screwdriver around the wheel to get the rubber even. The machine does wobble when on, and mostly from the top of the machine and not so much to cause me any concern.
I won't have time to take it apart and properly assess the situation until later this week. I'm not so sure the bandsaw is worth the hassle, since it's just a 12" Craftsman from 1978 that I bought on Craigslist for $25 (replacement wheels are no longer manufactured). I'd really like to just buy a nice, high quality (and high powered) bandsaw, but unfortunately it's not in the budget.
I will report back with a better description of the problem. My next step will be to clamp a steel rule to the frame to make sure the wheel is true. Then I'll spin check for balance as advised.