I doubt it could be a faulty tyre or wheel as they were all brand new when I bought the car and i've not smacked them/excessive curbing/pot holes etc. Not checked the weights so maybe one may have come loose or fallen off.

The car has only done 38k (its just 4 years old, this jan) and has never had a bump (to my knowledge) so that "hopefully" rules out any steering damage of any kind. Bushes however, are known to go early on E46's so that maybe a cause. if so, it'll be polybush time