Ok, to make a long story short, I purchased a new (used) car (2013 Subru Impreza) about ~ 2 years ago. When I purchased the vehicle, one of the only things I noticed that was "wrong" with it was that the front passenger side speaker sounded blown/buzzy/harsh/ crappy. So one of the first things I did was go to an audio shop and have them install 4 new door speakers. This was a great improvement from the factory speakers. However intermentally, I would still hear the highs sounding harsh/distorted, especially in rock/metal songs. So, I take it into another audio shop and have them install a new headunit (an alpine) along with a Sub and amp (the sub and amp are great) thinking that maybe there was an issue with the headunit (also, I wanted to upgrade anyways).
After this, for about a month or so, everything sounded pretty great, however occasionally I would still hear the harshness/distortion from the highs coming from the same speaker location at random times. Thinking maybe I might have blown a speaker (or, that I just didnt like the sound of the speakers), I went ahead and did some research and got myself some JBLs 64SQs and installed those myself, along with new mounting brackets. This did not make the issue better and, in fact, it made it worse (likely due to my unskilled wiring) and I started getting crackling and popping, on top of the intermittent harshness in the highs.
However, when I was installing the speakers, I did notice that some of the wires on the factory wireing harness were *badly* oxidized (like, brown brown instead of copper color). Thinking that this is likely the root of the issue, I went ahead and got some good 16ga OFC wire, and took it into another shop, and had them to a complete factory wireing bypass directly from the headunit to the speakers. This was a week ago. When I received the car back, upon pick up everything sounded great, the crackling and popping were gone and I was happy and hopeful that solved the issue with the harshness I was hearing in the highs intermittently out of that speaker.
That was not to last, though, and it doesn't seem like it solved the problem completely. Yesterday, for example, everything sounds fantastic and I even showed off the system to a buddy who said it was the cleanest, tightest system he has heard in a long time (and yesterday I agreed with him) however this morning on the way to work, the highs coming out of that speaker sound harsh again (metallic and "scratchy" sounding). One thing I *did* notice *this morning* is that when I turn my windshield wipers on, I get static noises out of that speaker, and that noise stops as soon as I turn the wipers off. Another thing is that it seems to get a tiny bit better if I turn my AC off as well.
And I am not sure where to go from here. I dont want to keep tossing money at the issue for it continue to be a problem. My next thought is that I need to redo the factory ground, but I dont understand why it's only impacting one location. My other thought is perhaps its a voltage issue and I need to replace my alternator (which i intend to put a 240 amp high performance alternator in there anyways)
Has anyone else experienced a similar issue or have any suggestions on what else I could possibly do? The biggest most frustrating aspect of this is that when I have time to go take it into a shop to have them hear whats going on to try and diagnois the issue, the system sounds generally great, so I keep getting looked at like I am nuts.
Any help/suggestions/insight would be greatly appreciated.