I have a VW Golf 1.9 GT TDI 'T' Reg (1999)

It has started making a whining noise which begins at about 40mph after couple of minutes starting from cold. It increases in pitch as the revs build up.

The noise stops if I ease off the accelerator and re-appears if I accelerate again.

It also stops if I depress the clutch as I am going along at speed.

The vehicle has done approx 147,000 miles. It has had a new cambelt at 120,000 miles and a new dualmass clutch at 130,000 miles.

The transmission oil is at the correct level and clean.

Any ideas ?