Loud Feedback noise coming from speakers

About 3 weeks ago I installed brand new 6.5 compenents and rear speakers in my car. I am running them off of a 4channel amp. Also, I have 2 subs running off a mono amp. Everything worked perfectly until yesterday. While I was driving a loud feedback noise started coming from all the speakers in the car including the subs. First thought in my mind was that maybe one of my RCA's came a loose. So, I pulled out the radio and checked and that was not the problem. Keep in mind I routed all my RCA 's on one side of  my vehicle and power wire on the other side. I checked the RCA's in the trunk to make sure they were ok and nothing seemed to be wrong. Ok, so now I am pissed because I can't figure out the problem. So, I started from scratch, and unhooked everything. I was just trying some things so I unplug the power harness from the radio. Now I have no power to the radio and I plug  one RCA in the input on the radio and still heard a feedback noise on that speaker. I hooked all of my RCA's up and all speakers had the feedback noise. So, I swaped out amps and it had the same problem on that amp. Has anyone experience this problem or have I overlook something else that could give me this problem? I'm lost. I'm thinking I have a bad set of RCA inputs on the radio but not for sure. I have a Pioneer 6400CD indash if that helps. Thanks for any help.