Car is in warrenty so if its this. This is replaced for free then?What engine have you got?
If it's a 1.9 then it's almost certainly the dual mass flywheel. The bearings in them go noisy and it changes noise with clutch pedal position.
This is an expensive job if you're not in warranty...
The bits alone are over £500 and there's 5 hours labour to get the box on and off.