I just installed a Legacy 720 for my interiors and a Hifonics bx1500d for the subs. The problem is that I am getting about 90% feedback and 10% music. I am using a aftermarket HU. The way I ran the wiring was to just use the original BMW stereo wires for the amp input. Wires are ran from the sub output from the HU and the speaker level outputs and feedback is comming from all channels. Any help will be greatly appreciated.