Grinding when switching gear under load

I think I might have a small problem. During normal driving it is fine, but when I press the clutchpedal under hard acceleration there is a grinding noise. My first thought was that the clutch is ready for retirement but it would make more sense if it was grinding when releasing the pedal. At first glance I couldn't see any damage to the cable. Is there anything else I could check before pulling the guts out of the car?