Big Green

I went to the dealership today to have a U0155 engine malfunction code checked out, and while I was there also had the HFL checked out due to interference (feedback based on RPMs). They came back and told me that my aftermarket amp/sub is causing the RPM feedback because it is taking up too much power (200watt RMS, 400 watt max rockford sub) and therefore the feedback is the alternator.

The dealership also stated that the engine malfunction code was the iSimple causing problems with the nav system. Obviously the dealership told me to take both parts out... not going to happen.

I had Best Buy install both, and I will have them look into both issues. I would, however, like to try and get some feedback from you guys prior to going over there, so they can at least have an idea of where to start. So, can anyone help me out? Thank you!!!