This was asked to be stickied cause it has helped a lot of people with grounding issues on their aftermarket headunits. The fix is quite simple. You take a 12ga wire and attach it to one screw at the back of the stereo and carefully wrap it around the RCA jacks at the rear of the HU. Of course you have to strip the wire and leave only a small bit at the one end of the wire. You will need two pieces of wire to complete this fix, but will make you a much happier camper with your new aftermarket car stereo.
Here are the photos. Remember the RCA plugins to the RCA jacks will help secure the wire so they will not come out or move out of place. Now if you are having problems with with your aftermarket HU and you are not using AMPs with your new HU, you can still do this trick, but the only difference is that you will want to a ground wire from the back of the HU to a solid ground point under the dash.
If you ever have any questions, please feel free to contact me here or via PM.