Geddy's resolution isn't the end all. Sorry...not trying to bust your balls :/
You aren't grounded properly somewhere and it's backfeeding into your system some how. If you have a Pioneer made in the last few years you POSSIBLY have an issue with a blown pico fuse inside the head unit. Geddy's thread will resolve that situation. Their internal fuse is very fragile. Plugging/Unplugging RCA's while the system is on will be enough to blow the fuse and cause an awful ground noise.
Geddy's fix will also help if you're creating a ground loop between your amps and the head unit.
Step 1) Use an Ipod w/RCA's to see if the ground noise disappears once you've disconnected the head unit.
If anwer is yes: You're H/U is picking up the ground noise. You can either run a wire to ground the H/U in the same location as your amps or try other techniques that you can research.
If answer is no: Your amplifiers aren't grounded properly. Did you ground them to your seat bolts? Apparently I've read that these can be zinc plated or something rather. Find a new location and use a nut/bolt combination that doesn't contain zinc. Otherwise, you're not grounded properly.
This is just a start and there's a million different issues that it could be...sorry :/ Chime in with updates from your trials.
