We had a problem with a knocking sound on our 2005 Toyota Avensis. We extended the warranty in September 2009, and had the car serviced and MOTd under their terms. We were shocked to hear that we would have to pay for a four-hour diagnostic service to find out whether it was a broken gearbox bearing or if it was wear and tear, in which case the warranty wouldn't cover it. Would it be better to have the £750 refunded and go have it done at a specialist garage?