since no one else replied I will try. I think its the head unit, but it might not be. I dont have a direct answer for why its cracking, but that doesnt normally happen. Bypassing the amp wont do anything but reduce wattage. (like you said). This might sound stupiod but check the pos. neg. connections and make sure they are right. might sound stupid but it makes a big deal. Ive been drinking, but I still think that itsw not normall.
I've had speakers pop and wine when the car turned on before, and even when you hit any power button's. I ended up baypassing the amps. I really don't like changing the factory look but it's what had to be done.
Does it only crackle right when he starts the car? Or is it always making the sound. If it is only a quick poping noise it should be easy to fix by adding a resistor on the remote turn on lead. If the noise continues for a few seconds this method will not help and you probably have some bad equipment, or possibly a bad ground path with something. Having speakers wired out of phase (pos and neg backwards) will not cause that type of problem. I'm not too sure about the Mach 1000 system, I have been installing for 11 years and have never had one come through my shop...
You need a voltage regulator. The Pioneer puts out 12 volts to the amps, but the Shaker 1000 only needs 5 volts..
I installed the Pioneer AVIC-D3 in my car, with Shaker 1000, and do not have any popping.
They are available at Radio Shack.
For more info, see my AVIC-D3 write-up.
http://forums.stangnet.com/showthread.php?t=731487
No one else knows about the voltage regulator??
Here is the voltage regulator installed:
Single blue wire is FROM the head unit, gray is ground, and the two dark blue wires go out to the factory amps (via harness that connects to factory harness).
And here it is at Radio Shack:
http://www.radioshack.com/product/index.jsp?productId=2062599&cp
http://i19.photobucket.com/albums/b169/mustangparts65/AVIC-D3/DSC01993.jpg
Single blue wire is FROM the head unit, gray is ground, and the two dark blue wires go out to the factory amps (via harness that connects to factory harness).
And here it is at Radio Shack:
http://www.radioshack.com/product/index.jsp?productId=2062599&cp
http://i19.photobucket.com/albums/b169/mustangparts65/AVIC-D3/DSC01993.jpg
Hmm... technically yes.
I would still make a safe bet that the Shaker 1000 and Mach 1000 are similar in terms of the voltage they require to turn-on.
I was only making a suggestion.. It sounds to me like the exact problem one would experience when not using the voltage regulator.