bet your trackings out mate and you may not have noticed it on the worn tyres perhaps because one was low on pressure or had unevenly worn compensating for the tracking issue.

or the wheels havnt been refitted propperly. unlikely i know, but may be worth taking them all off, cleaning the wheels and hubs, light smear of copper grease and refit. if that doesnt make any different just go get the tracking checked, bet its out!