A4 TDI 1.9 Sport Auto vibration - please help!

Hi all

I've got a 53 plate Audi A4 1.9 TDI Sport estate and whilst driving from Bristol to Cambridge the other day it developed a vibration and I'm really struggling to decipher what is causing it. It's driving me nuts so any help will be most welcome.

It started after a dual carriageway section. A vibration felt through the steering and throttle pedal almost as if the front tyres were out of balance. It only occurred whilst under load, cruising at around 60mph. It seemed to be not as bad at low speeds and similarly if I went up to 80/90 it also more or less disappeared. If I let off the throttle it disappears completely so I know it's not a wheel bearing.
It's an auto box and i've noticed that whilst waiting at traffic lights in 'drive' with my foot on the brake pedal there seems to be a very slight vibration which could or could not be related...

A quick look under the bonnet doesn't show any obvious problems (apart from the front belt looks a bit ropey) so I'm a bit stuck really...

Sorry it's a bit vague but I'm hoping that it might be a common problem that one of you guys can spot straight away. :1zhelp:

Cheers Ian

Have you scanned for fault codes yet?

Check the wheel balancing mate!!

did you find out what the problem was?