The floating ground adapter converts the RCA outputs into floating ground, which is what I'm told the Bose amp expects to receive. One tech explained that inputing a regular chassis ground to the bose unit exposes the amp to every little change in voltage (even tiny ones) which causes the popping sound. Isolating the ground should therefore fix the problem.

2 techs independently recommended this to me now, and it was their very first inclination - they seem to have seen this before. I plan to try it next week.

SIG STARTS HERE
2003 Audi A4 Avant, Black/black
3.0 V6, Sport, Manual

"Mods": all-round tint, 35% front, 20% rears; sedan sport rims; clear corners; yellow fogs; V1 hardwire/concealed display; XM Commander headliner install; emergency lights/radio; Pioneer AVH-P4000DVD with stock Bose system