08 WR250R with about 1000 easy miles. Today I went to a motopark that involved deep sand, steep banks, turning around in deep sand and slush, and some pretty tough stuff. When turning around in the deep sand, with feet on the ground and spinning rear wheel to work the bike around, it sounded like the front sprocket was letting the chain jump a notch. This also occurred when fanning the clutch and getting up a very steep bank a couple of times. I plan on pulling the cover off and looking at the front sprocket. The other guy with me, a very experienced motorcyclist and WR250 owner, said the same thing when he heard it, that it sounded like the chain was jumping a tooth on the sprocket.
#2: at low speeds, I have noticed a squirmy, rubbery squeek. This could be on a smooth surface or whatever, sounds like two pieces of rubber rubbing together, or tennis shoes on a gym floor or something. Could even be knobby squirm on pavement?