Hissing, whiring?

[Tps2889]

2006 A3 2.0t fsi.

I’ve got a strange hissing noise in the car, it only happens when I’m in gear and when I’m not touching any pedals. 
As soon as I touch the accelerator, even a tiny bit, it disappears and when I press the clutch in fully it disappears. 
I don’t hear the noise when I’m in neutral or going below 10mph

Any ideas? I’m baffled?

[cliffcoggin]

Normally I would suggest an air leak to cause a hiss, but that would not be affected by clutch operation. Perhaps you are hearing the start of some belt slippage.

[Tps2889]

I had the cam and water pump done a couple of days ago. Could it be alternator? There’s no way to check, because when it’s sat idle it ticks over lovely.

[cliffcoggin]

Yes, press the belt inwards, it should barely move.

If the noise began immediately after having the cambelt and water pump done I would be suspicious that something had been neglected in re-assembly.

[Tps2889]

Thank you. I’ll speak to the garage!