The central locking, backups, and some other things like bolsters/headrests/and trunnk gri are controlled by a assembly under the rear passenger seat. If you can hear it run for the central (inside) hose might have loosend, and can be replaced. The star has a article on it in avery recent issue. Check fuses first first these pumps are not cheap, but dont go bad as often as the (pull in doors and trunk) pump which is common