Car wobble

Out of balance is more of a shake and usually at higher speeds than 30 MPH. Wobble (side-to-side) can be caused by uneven tire wear and/or failed belts where the tire no longer runs true. Do you feel the wobble in the steering wheel or more seat of the pants? You should have this looked at by a tire shop ASAP - although you don't feel it as much (or at all) at higher speeds doesn't mean that there isn't a problem. Obviously, you wouldn't want a tire coming apart at freeway/highway speeds. By any chance have you smacked a curb lately?

+1. Lower speed wobbles are either out of round tire or rim!