Thanks for the replies. I've tried the rebalancing already with no results. I might want to describe the shimmy as wheelslapping where both wheels shake back and forth in unison. Tapping the brakes or turning will usually stop it. This happens at low speeds only so far and usually when I hit a bump in the road. I've never seen this before except on a shopping cart like you guys have mentioned , and I don't want it to tear up my front end.