My 2002 Sprint RS occasionally exhibits some very strange handling characteristics. It only has 8k miles on the odometer, and about 400 miles on a new set of ContiMotions, which I had mounted at a local shop. Every so often I get a very disconcerting feeling that something is loose under me, to where the bike feels "squishy" while riding straight ahead at relatively low speeds, 25 to 40 mph, as if I just hit a small patch of greased ball bearings. I have checked my tire pressure, which I run at 42R/40F, and neither was low. I don't have a center stand, but gave everything a good shake while it was on a lift at the shop, and felt no play on the rear wheel or swingarm. The weird thing is that it doesn't do it all the time! Anybody have any idea what could be causing this? It is a very bad feeling, which doesn't inspire confidence at all, even though it generally feels solid. Any ideas would be most appreciated, thanks!
PS. the previous owner treated the bike terribly, and dropped it on both sides at least once.