I have a 2006 Hyandai Elantra (90k). After about an hour of highway driving (never before an hour, but sometimes not even after 2 hours) the car gets a serious shimmy like a wheel balance issue. The shimmy only occurs at highway speeds. The shimmy get slightly worse when I let off the accelerator and when I brake. The car also seems to lose some power when this shimmy starts, but that may just be the side effect of the shimmy. The real kicker is that when I pull off an exit and come to a stop (or get into stop and go traffic) and then return to highway speed the shimmy is gone.
I thought maybe a wheel bearing or a shifted belt, but I have ruled those out. Any suggestions?