Okay... this is long but I want to be thorough so everyone will know what I did and did not do. Here's how it has gone so far this morning:
I pulled out the HU this morning and connected my mp3 player up as a source. When I did this before, like a tard, I left the Pioneer HU connected in order to get the remote feed. This time, I tapped the remote feed into another 12v source to get the amp to turn on. When I did this, I still had noise. Next I took a pair of plain-jane RCA's (instead of the streetwires that I had) and ran them outside the vehicle to the amp. No noise. Of course, I could only run one set at a time so I just ran everything into the rear first and then the front... no noise at all. After that, I pulled the 860MP HU from the truck and used it with the plain RCA's. That checked out okay. I tried the new 590IB unit and that checked out fine too--I didn't hear any noise in the system. During this check I was only doing either the front or the rear channels, but not all 4 together. From that point, I stripped everything out the car, pulled the streetwires and tried the same thing with them. I was thinking that either the RCA's were faulty or I made a mistake by running them through the middle of the car under the console. What I found was that the Streetwires produced noised without having them hooked up to the HU, as odd as that may sound. I just held the RCAs in my hand and noise was produced. Without using a HU, I did the same thing with the cheap plain ones (and thought back to an earlier reply to this about how someone goes with the cheapest RCAs he can find) and the cheap ones did not have noise. Again, I was connecting them to one channel at a time. So, I decided to run the plain ones and not the Streetwires. I did that, both sets all the way to the front, to the hood release. I kept the car running while I did this and had both sets (all four channels) connected, just to listen in case noise popped up. When I got to the hood release, I connected them to the 860MP HU and low and behold, there was noise.
After cussing a bit, I moved the RCA's out from where I just ran them. I noticed that depending on where I held the RCA's (this is all on the drivers side), the noise grew louder and would return to the normal volume... strange. I was thinking it was interference from something but I couldnt think of anything that would cause that. I went an rechecked the RCA's one set at a time and found out that both sets were fine... on the rear channel of the amp. However, when I plugged in the front side after the rear were already connected, noise was produced out of both front and rear speakers. I disconnected the front set from the amp, the noise went away. I swapped the RCAs at the amp and everything was still cool though I kept thinking I was hearing a nearly inaudible hum. When I connected all four channels back, the noise returned. If I kept just the rear connected to both the HU and the amp and the front connected to the amp, the noise was there. This happened no matter what set I used on the front. Noise was present regardless. This also happened if nothing was on the rear but the front was connected AND the amp's "signal source" switch (I call it that b/c I dont have another name for it) is switched from using both Front and Rear signals to using Front only. If set on using Front and Rear, the amp works without any apparent noise on the EITHER the front side or the rear side BUT NOT when all four channels are used.
I tried grounding the shields of the RCAs. That made the noise worse. I did this at the HU. I did not go back to using the mp3 player as a source b/c with it, I could only do one channel or the other and I already established that the rear worked great but the front side didnt. Also, I tried using an PAC SNI-1 on the front channel when all four channels were being used but that didnt do anything.
So... what now? new amp? It is a coincidence that I had such a similar problem with the Rockford 551x. I ended up having to bridge everything off of one channel until I could get a different amp. If there is a problem in the amp, is something I could look for and fix?