Re: 2001 hse radio problem
if it's a 2001 its a P38, with the Alpine-headed H/K system - with DSP by the sounds of it.
The system is run by a single amp that lives behind the soundproofing that is behind the subwoofer inside the rear left cover in the boot. Effectively, the HU just acts as a remote control when plugged into a DSP amp as it is the amp itself that controls gain, volume, etc. They are known to fail after some years, giving the symptoms you describe. The failure is usually caused by moisture ingress corroding its internals, however sometimes it is only the connector that corrodes, so sometimes a removal, clean and reconnect cures the issue.... if you're lucky, that is...