Radio turning on and off

[t400]

Recently my stereo turned it self off whilst I was at a junction
and turned itself back on 10 seconds later

Now it can do it EVERY SECOND

ON OFF ON OFF

the time on and off is random, and after a while it will stay on.

Its especially problematic at the start and end of a journey.

It even will turn on after the key is out the ign, and Ive locked and left the car

Whats that about?
If it was a fuse, would it turn on at all?

I have a standard H/u, HK, Sat nav and a car phone kit which have been problem free for over 2 years.