Help required please!

[Angry Koala]

Whilst I'm extremely happy overall with my new car the stereo is really starting to get on my t*ts!

When I bought it the guy said that when he had taken the car out the garage after 6 months the stereo was playing up with interference. I tried it, it worked fine. 400 miles later I had had no problems with it at all (bandwidth expander seemed to work fine and CD player was perfect).

Next morning I switch it on and go deaf with the worst hiss/crackle I've ever heard - I thought maybe it was a loose aerial connection but it was doing the same with CDs (also makes a noise as if scrambling CD's).

Anyway me and Baz took the dash off yesterday to get to the stereo to try to find the cause. Checked the earth which appeared fine, rewired the live feed and insulated it properly as it had previously been poory soldered and taped. Nothing solved it until we disconnected the bandwidth expander and then everything worked perfectly. Thinking that was the problem and I needed to start looking for a new B.E we put everything back in and it worked fine. 2 minutes up the road switch the stereo on and it's all gone wrong again.......

Unit is a double din Panasonic jobbie.

Anyone got any thoughts please cos it's driving me nuts?!?!