Your battery is still dying? That would indicate either an alternator issue or something else there.
As for your high pitch whinning noise. The fix I used is quite simple and should work for yours as well. You just cut a piece of 12-16ga wire and trace it around the RCA jacks of the HU.
Here is a picture to what I am talking about. I did this to my Pioneer 5000 HU. It has worked wonders for many others out there, and it is not GP specific related.
If that does not work, then there is an issue with the HU, there are internal fuses that sometimes blow and they have to be repaired by expert/trained electronics tech to replace those tiny fuses inside the HU. Honestly the never bought the whole changing spark plug wires theory for the simple fact I am currently running PRJ 10.4mm wires, some of the thickest and best made wires out there and when I replaced my stock HU with my Pioneer 5000 HU, the whine was immediate. It wasn't till like 6 months later I learned of the above pictured method to resolve grounding issues with my HU. As stated before it works on other HU's besides just Pioneer HUs.
Good Luck![]()