I have noticed a noise in my 2002 1.9 tdi 90. It is there as the car idles, and goes with increased acceleration. Its like a whine. The timing belt and drive belts have just been changed, but I'm fairly sure the same noise was there before. A bit noiser though. Could it be a wheel that drives the belt, or a pump. Car is driving spot on. No other problems.

Alternator?

If belt is tensioned too tight can put a strain on the alternator.

The belt is tight, but Im not sure if its too tight. Can I test electrically? The noise was there before the belts were changed, but has got worse.

Still think maybe alternator?

On my last car after the belt change it used to whine on increased acceleration.It never did any harm and i did another 50k before i sold it.

I have tested the voltage with lights on, heater on etc and it seems to be reading around 13.8v. Would VAG COM give an error?

I think once you get your timing belt done correctly(other post youv'e got)might stop your whining.