Have you carefully checked all wiring and connections, especially the wires going into the back of the sled harness? Have you tugged on all connections (both your connections and the ones on the sled) to make sure there's nothing loose?

Refresh my memory: Is this problem with a brand new installation of the player, or did it work fine for a while and then the noise suddenly appeared? What was installed in the car prior to having the empeg player installed in the car?