I installed a Soundstream Bluetooth amp and 4 Polk audio speakers. They play when I turn the car on through my iphone. The issue I have is when I turn the car on the speakers will crackle for a second as well as when I turn the car off. Any suggestions on why this is happening. The amp is hooked up directly to the battery, there is also a keyed power wire that is hooked up as well.

Thanks Craig