HU cycling power

I am installing a Pioneer DEH-1500 which has given me a couple of issues. I was able to resolve the first issue in which I was seeking a value for the 12V constant inline fuse which was not provided with the wiring harness. I tried a 5A which seemed to work out. After listening to the stereo for about a half hour the second issue developed. Now, my second issue involves the power being cycled on/off about every 2 seconds. The HU will power up, screech and power down and repeat. Upon, disconnecting the speakers the screech still occurs from within the HU. HELP!!!!! I have tried to find a better ground which does not seem to help the situation. Should I disconnect everything minus the 12V constant and switched power? Or what kind of troubleshooting is possible?

Sounds like a defective unit if the noise is actually coming from the unit.