So on my way home from skiing a few days ago the steering wheel in 503 started shaking back and forth at a frequency that tells me it's an imbalance issue with the tires/wheels. It was pretty mucky out so I assumed I had some snow stuck in a wheel. Well, the car sat in the garage overnight and the next day it was fine. That night though, it started doing it again, as well as today. Drove to get some food, it was fine, on the way back, it started shaking again. WTF? I pulled off both front tires and had a look. Everything looked normal to me. Tires in good shape, no caked on mud or snow in the wheels, etc. It's not a lost wheel weight as it's a much bigger shake than what that would cause and it does it at really slow speeds. Like cruising through a parking lot at less than 10mph I can feel it. It jerks the steering wheel pretty good, more to the driver's side. Problem is intermittent so I'm confused as hell. Anybody got any ideas?