Whirring noise coming from somewhere

[Iyse]

Whenever I'm in gear travelling at over 1500RPM in my 98 W202, I hear a whirring, whistling noise which I think is coming from under the bonnet, as I can hear it with all the windows closed and seems to be coming from the front. If I depress the clutch, it disappears but re-engaging gears brings the subtle noise back after half a second!! Please someone tell me what it is, it's driving me crazy!!

 

[Vlad]

If it goes when you dip the clutch pedal, this normally indicates a noisy clutch release bearing, which can only be fixed by getting at the clutch.