I had 'drumming' tyres with my Volkswagen Golf 1.4 TSI about three or four years ago. It seems that the rear tyres wear in a 'scalloped' pattern and that causes the noise - not unlike a failing wheel bearing. Volkswagen said it was a not uncommon occurrence. I had the tyres swapped diagonally front to back at each service and that solved the problem. As a bonus it meant the tyres all wore out at about the same rate so I got a full set at renewal time; I don't like to mix old and new.