Just removed the Concert HU from my '98 A4 Avant. I've not used a harness adapter, just wired it in myself.
I've wired the rear speakers into the normal Sony HU wires and put the OE Amp feed onto the AMP Remote wire from HU.
I've got sound coming out of all speaker inc OE sub. (will be fitting my amp and sub at somepoint and removing the OE amp and sub)
I keep getting a loud crackling noise through the rear speakers and amp only. It's like a spike or surge. Very annoying as it distorts the sound of the music when it happens. All wires are nice and secure etc.
Any ideas what is causing this spike? I've turned the bass right down and it still does it.