really strange PPI amp malfunction

I'm almost ready to call it quits...   I got everything reinstalled and wired up. Now when I connect the Sub-out rca's to the amp there is a high pitched constant noise coming from the amp itself. It seems like the amp runs fine if I just hook it up to a regular walkman and use that as the source.

You have a ground loop if you only grounded one side of the rca's. Ground both sides- at the amp and at the radio and see if your noise goes away.My ex once told me I have a perfect face for radio.

this is how everything is hooked up now: 4 gauge power wire from the battery + to the amp + terminal. 8 gauge wire from the main grounding point under the dash to the (-) amp terminal The head unit, rca shields, and amp are all grounded at the same location under the dash. I soldered a wire to the ground shields of the other end of the rca cable and connected the wire to the ground terminal on the amp. So I ran the stereo without starting the car and everything seemed to work fine aside from the loud sub pop as soon as I turned it on. I did notice that as I increased the volume, I started to get bass distortion in all of the interior speakers, despite the fact that they are crossed over at 125hz and I never had this problem before. As soon as I started the engine the sub went out of control again popping loudly so i shut if off.

I see a replacement amp in your near future.My ex once told me I have a perfect face for radio.