[rogerthechorister]

I've been thinking about this. It's been OK for several days now, and hundreds of miles (North Kent to Croydon, Croydon to Wood Green, local running and back - a whole tankful!) but I'd still like to get to the bottom of it.

My current thought is that all the door speakers and the A pillar and D pillar speakers go off at once. I think (haven't checked yet) that one side of every speaker is at earth - not locally but somewhere in the dash. So if I have not got a good earth, all could go off at once. So I'm first going to test that there is one side of every speaker that is at earth (easiest place will be behind the head unit) then make a good earth to the head unit casing.

Then wait and see if it goes funny again.