Don't know if this a connected problem (no pun intended) but on last service it was mentioned that the rear anti rollbar bushes would need replacing at the next service as they were beginning to deteriorate. That was about 3000 miles ago but recently I've noticed an annoying oscillation coming from the rear of the car. Only really noticeable on flat roads and at higher speeds as it varies with road speed. Not intrusive but getting annoying. A friend said it may be the tyres, they have been on for about 15k now but still loads of tread, so I'm wondering if the roll-bar bushes may just be transferring the noise from somewhere.

Anyone come across this and have any ideas?