Renault Kangoo van 55 reg central locking?

i have a 55 reg kangoo van and seem to have a problem with the locking system. The doors randomly lock and unlock themselves repeatedly for sometimes hours on end and other times just for a few minutes. it doesn't matter whether the engine is running or not, or whether the van is locked or unlocked to start with. i haven't a clue what the problem is any help appreciated.