bose factory amp, audi quattro

I was wondering if any of the other installers on this site have come across an issue with Bose factory amp in an Audi Quattro when installing after market Kenwood radio. I used a Metra harness for VW / Audi with factory amp. After hooking up all wires in harness, antenna adapter, RCA's and all, It turned on and sounded ok until... I changed the source and the speakers made a popping noise. I thought it had something to do with the remote turn on but I put a relay with a diode to stop any pops. That didn't solve the issue and I then tried to use an ignition source to turn it on. That did nothing to fix issue either. I also had installed a Bass tube but that had no noise, no pop. The only thing I didn't do is find a new ground and not use the one in the harness. Have you had any issue like this? What did you do to fix it? Anyway I was frustrated and the customer was coming to pick her car up so I did what I had to do. I took the Kenwood out and figured out what wires on the back were for the rear out to the factory amp. I soldered onto these with some audio cable I cut and used couplers to make them into female. Wired that all up and plugged the radio in and turned it on to see the word "SAFE". Could my day get any better? I was sure the customer would not know what the code was and I would have to call an Audi dealer. To my surprise, she had it written in her owners manual because she had to use it once when her battery was replaced. We entered the code and the radio came on, hallelujah. The bass tube came on and the bass sounded pretty good considering it was a last resort effort to keep a customer happy with at least part of what she was to have put in. I had thought that this was going to happen but I was hoping I was wrong at the same time. Factory amps and trying to add to them are kinda a pain in the butt.

Have you tried the resistor on the amp turn on wire like the old mustangs.

no I didn't try that. What value resistor would work for it?