Do you get stray signal noise when there's no active audio signal, and/or a turn-off thump? Mine does. I used a PPI 900.5 which as far as I can tell is sold as several different 'brands', Soundstream being one of them.
The stock UQA amp has a mute function, active whenever the head unit isn't outputting a true signal. For instance when radio is on, volume turned to 0, the mute pin triggers (~5VDC), which shorts the low level inputs and kills any stray noise on the lines. I have a rough design for a DIY adapter that does the same thing but haven't got around to building it yet.