Possible incorrect grounding when installing new car stereo. Need help.

I installed a Boss 612 car stereo into my 2000 Jeep Grand Cherokee. After installing, a crackling noise comes from the speakers as well as the radio station. The original factory Jeep stereo had a 6 disk changer in the back, however, the 612 does not have the option. The 612 had wires for the electrical, ground, ant, and 4 speakers, however, there were leftover wires in the Jeep which I had to cap. I may have grounded the stereo incorrectly. The Jeep stereo had a seperate black wire that may not be the ground. Not sure. Any suggestions would be greatly appreciated. Thank you.