I have a DVD surround sound system situated in an outhouse with its own electrical sockets. I leave the unit on standby. For the last year the unit has been switching itself on to a certain radio channel and playing that channel.It is so random that it might not occur for weeks on end but then it could happen three or four days or nights on the trot. This last week it has occurred nearly every day. When it last happened I switched it off but switched it to the aux mode. Lo and behold the next day it was on again playing the self same radio channel.

Any suggestions?

More than likely your system is "seeing" random IR signals from an outside source.

A simple test is to turn the unit 90 degrees, I kid you not.

Or shield the IR port with an al. foil strip when not in use.