High pitched whining when head unit is on. Intensifies when accelerating. Buzzing sound when switched off, even when engine is switched off.

Hi GuruCY7, it sounds most likely that you have an earth problem somewhere on the car, or possibly that some of the speaker wiring has worn through and is shorting out on the car's body. It's also possible that there's a fault with the car's alternator, or an internal fault with the car's head unit. I'd recommend getting it to an auto electrician and hopefully it won't be an expensive fix.

Thank you for your response. I have already booked it in with an auto electrician. As you say, let's hope it's not too costly a repair.

Good luck, and do let us know what the fault was as it may be helpful to ther owners on here. Bob