Mach system install

I have installed aftermarket cd players in 2000 model mustangs equipped with the Mach systems. I hooked both up using the required wiring harnesses. I hooked up the amp turn-on from the cd player to the wire that turns on the factory amps in the car. Everything sounds great except when the systems power turns on it makes a loud popping and high frequency pitched sound when it comes on for about one second.  Both cars do the same thing. Could anyone tell me what this is and how to fix it? The sound is ear piercing and gets on your nerves.

Ford uses a 5-volt turn on in their factory amp'd systems.  Your new decks use a 12-volt turn on.  Wire in a 1.5k ohm resistor inline and call it good.My ex once told me I have a perfect face for radio.

it is the level that the amplifier is producing, you need to use low-level imputs, there is a harness that metra offers that has rca pre-outs that are already wired as low-level, this will lower the noise but may not completly remove it, if this is the case, use a better ground that the factory supplied, at both the deck and factory amp. after trying all of that and you still have noise hook up ground loop isolators they plug into the rca's on the deck and plug into the harness that has the rca's that metra offers.sweet.