Gearbox problem on my C4S??
 

Ever since I bought my dream car, an 02 plate Porsche Carrera 4S Coupe a few months ago, I am constantly hearing a mysterious 'clunk' noise whenever I release the clutch after changing the gear ( sometimes just by pressing the clutch on the move). My local Porsche Centre has fitted a new gearbox, a new clutch plate and a pressure plate, but the noise won't go away. Although my car is booked in for yet another inspection, I am beginning to lose faith in my local Porsche Centre. What is causing this noise and how can it be cured? Has anyone encountered similar problems? Lastly, I would like to know if it is possible to ask technicians from the Porsche headquarters to check what the problem is.