radio problems

[spenburge]

after recently buying a 2001 x5 i am having problems with the eletrics inside either the sat nav ,phone or radio here are a list of the problems if anybody can tell me if they could be related to each other i would be much appreciated.
1/ radio just goes off with no warning at no specific time and no specific length of time but seems to come back on with a play with the sat nav and switching it on and off. all audio is lost when it goes off including sat nav voice and cd player.