could be the release bearing, this happen on my Punto, when you put the pedal to the floor, there was a noticeable rattling. This noise eventually went, to be replaced with a rattling when the car was in neutral- the rattling went when you depressed the clutch. 20,000 miles later the bearing finally went leaving me with a very creaky stiff (ooer) notchy pedal. Had a new clutch fitted but I still get the rattle in neutral. Alberto's motors (alfa specialist near Oldham) checked it- just said it was naturally rattly!