Hearing Scratches while calling

Hi to all, i have and iphone 4 and suddenly 3 days now is doing scratches while on call so none can hear me.they hear the scratches and also i hear the scratches too.then if i hang up and try to call again sometimes works fine sometimes not!also i realised that if i try to touch the metal part harder fixing the sound but again after a while is doing the same!i have changed ear speaker but still the same!does anyone have any idea on how to fix that?do i have to change audio IC?

thank you in advance!