Thanks for all your input, i will coninue investigating this weekend. If i find anything i'll let you know.

I have finally got round to tackling this problem as it has got a lot worse and the audio from the stereo/sat nav etc was hardly working at all. I decided to disconnect the battery as a precaution and then remove the radio module BM24 in my case. The plug connection was secure, but i undid it and cleaned the connector sockets in the plug with a small file (although they did not really look corroded) as a precaution also. Idisassembled the unit to inspect it for any obvious issue such as loose components, or burnt out areas but found no problems. On refitting and reconnecting the battery after approx 1 hour i have found the stereo to functionn without fault for three days so far. This appears to have sorted the problem for me but a few more test days will prove it for sure. Here's hoping. This is an easy thing to do and i recommend it before replacing the expensive radio module.