"Flat-spotting" was a problem when nylon tires were first introduced (I know, I'm dating myself). In more modern times, although tires can still get flat spots, they round out very quickly with a little driving.
Another possibility is that the tires have developed a tread bubble or sidewall bubble. Sometimes they just do, for no apparent reason. I seem to recall that wmtire posted about these a few months ago. In theory you can identify these by running your hands over the tread and sidewall (it is always the inner sidewall!), but I have not had very good luck doing that ... It might be worthwhile to pay your mechanic a couple bucks to put the TM up on his lift, so you and he can do a visual inspection.
My money is on unbalanced wheels/tires. It has been a relatively common problem with TMs of that age. The factory seems to be dealing with it today. I think it is unlikely to be trhe axle, but asa Scott points out, it might very well be new tire time. Your opportunity to upgrade to 15 inch tires!
Bill
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