Stereo shuts off when its loud?

Just installed a Sony MEX 1HD deck into my Malibu. Its wired into a 1000 watt 2/1 channel Sony Xplod amp. It plays fine and can get pretty loud on FM, but HDD and CD I can only get so loud and it shuts the power off to the head unit? It attempts to restart itself, but shuts itself off again until I turn it down. I know this unit and set up can push louder - am I missing something? It never did this in my truck (where the deck came from)- but it wasn't hooked into an amp then either? The old Sony head unit pushed louder with no problems (until I soaked it in a Florida monsoon...)
Help?