Hi. The central locking on my 1999 golf GTI seems to have developed a fault. The back doors will not lock or unlock with the key or the remote. This is an intermittant fault as sometimes they decide to work but not vey often. The drivers side back door works the most fequently but make a noise when working. I Have owned the car for six years now and have had all four door locks replaced in the past none of which are still under warranty. Any advice would be greatly recieved. Many thanks.