sonix sells that HU for 120... maybe try lowering your price...?
http://www.sonicelectronix.com/item_11104_Pioneer+Premier+DEH-P400UB.html?gclid=CO_OxJfNnJsCFSQeDQodvhh3qg
i had an amp that did this one time a few years back, no matter what i tried it would always cut in an out with more and less power. i ended up just getting rid of it.