I installed an amp with a sub using the PAC AOEM FRD24 harness. Everything works great, however sometimes the volume starts to fluctuate......I can see the bars on the display move back and forth just a little (then "artist" and "song" title reappear). I have to use the steering wheel controls to set the volume again because the volume **** makes it go crazy. I have the amp running the sub off the rear channels (bridged) and the front speakers off the front two channels. I tied into the harness for the front but at no point does the amplified signal have a path to the headunit because I was sure to cut the wires in the harness. Any ideas what could be causing this?