Originally Posted by CalebCasias
Do you know the location of the ground wires?
Well not exactly because every installation is different. On the H/U it will be the black wire coming out of the unit, normally spliced or solder to the factory ground wire. Unless there is a bad splice or solder joint this is normally not an issue.
The amp ground normally will be located somewhere near the amp. Hopefully who ever installed it prepped the ground well, removing an paint between the ground lug and chassis. You don't want to just count on the the nut or bolt providing the ground path.
The next thing to check is the RCA's. Take a look at this video on how to do this:
This normally happens because we screw up, we work hot and during our connection process grounding the center conductor and blew the fuse. You can take the radio apart or send it in to have it fixed but the simple fix is to ground the RCA to chassis. It doesn't need to be a big wire as shown there.
If everything checks out and the noise is still present we still have 2 more things to check for and that is RF noise, one caused by the engine and the other caused by the electrical system.
Engine noise, if the interference goes up and down as the engine is rev'd this is normally engine RF induced through the power leads to the H/U. What you would do here is hook up a ferret core filter on the power lead to the H/U. FYI I have not seen this be an issue on a modern car for a long time.
The last thing to check is electrical system RF noise. This normally happens when you route your RCA's and amp power cables together. Always best practice to run them either side of the vehicle. But all is not lost if you RCA cables came with a 3rd connection called a drain. The idea behind the drain is to is to shunt the noise to ground and in most cases it works great. On the H/U end of the RCA hook that wire up to ground and leave the amp end un-hooked. Some people like to use these wires and the amp remote turn on but unless the RCA specifically says it can be used for that purpose don't.
Remember that less is more here. Work thru each one at a time to find the problem. In the end if none of this proves to be the problem you have a bad H/U or amp.