Originally Posted by DSB335d
I agree. I've taken my Subaru off road several times and some mud packed into the wheels caused a vibration, drove to the nearest self serve car wash and cleaned out my wheels.
Sounds like it to me too.
The give aways of possible packed snow/mud was he had to rock the car to get it out and it was also in a parking lot with 4-5" of snow and he couldn't drive any further.
Wash the back of the wheels.