Clutch pedal thud ? On release past clutch disengage

My superb tdi100 has developed a thud with the clutch pedal when you release it all the way like the pedal box is loose ? I feel a thud back through the floor / brake pedal and the pedal feels loose someone told me its a common thing but can't find anything on here about it . The clutch is fine it's the last bit of travel after the clutch has disengaged like the spring is pulling against the loose pedal ?

Need to get the dash off etc for a look but wanted to ask on here first as its doing my nut in !