Thank you all for your thoughts. He only has 1400 miles on it. He's pretty sure it's not the pavement, no big or small ruts in the road when it's happened. He does keep 40lbs. of air in the rear tire. He took it back to the dealer yesterday and hasn't heard anything from them yet. The other 2 times he had it in, they said the only thing they found was the shock bolts were'nt as tight as they should have been, but it has done it again since they tightened them. It mostly seems to do it going straight, not on curves. The last time it pushed him left of center and wobbled till he got it stoped. Not sure what the dealer is going to do now. Thanks again for all your suggestions.