1.9 TDI Serious Clutch Pedal Vibration

I drive a 2000 A6 1.9 TDI that has developed a vibration that can be felt through the clutch pedal. I'm after any opinions on the possible cause before I get fobbed off by a dealer.

Symptoms are :-

Clutch bites high, but I understand that this isn't unusual
Vibration is directly linked to engine speed.
Can be felt by just pressing the clutch 5mm, right down to the carpet.
No slipping problems
Engine is running smoothly.

Any clues appreciated...

I could live with that, but this one doesn't go away. It's there even when the pedal hits the carpet.

It's 'duh duh duh duh duh' at idle and 'de de de de de' as the revs increase. In gear or neutral, moving or stationary.