hey guys, noticed a boom / drone sound from the exhaust on our a3 140 tdi quattro, it seems to be quite loud when on motorway driving, when accelerating between 70 and 80mph, it seems to go away if i drop into 5th gear even at same speed, but droney again in 6th gear, has anyone had this same thing or is it maybe a characteristic of the a3? or maybe yet another fault to report to glasgow audi