My electric/electronic story is not about the sound system.
The car in question was a hard-top convertible. In the dead of winter, that convertible top was fully up and in cover mode, and it stayed that way.

It was my car until last month.
I was driving about, minding my own business. I parked briefly, got out, ran an errand, got back into the car, and started the engine.
A screaming-meemies beeper, which had never gone off before, began to beep, I don't know how many times per minute, anyhow it was a non-stop beat of a beep.
The message on the dashboard said that the car top, well I forget now WHAT it said, but that it needed to be properly closed. Of course it already was properly closed, but the beeper beeped anyhow.

That car, I bought from a full-service dealer with a service department, and always had the work done there where I had bought it. So, fast forward to the service department at the dealer's. I won't even go into the staffperson who did the paperwork, who is an immigrant from Brazil, first language is Portuguese, and they and I had a bit of a comprehension problem.
The servicepeople checked out that electronic beeper alarm and right away were very serious. Not regarding the convertible top, which everybody could see was the way it was meant to be. No, we have to find out why the alarm got triggered when nothing is amiss with the top. And this is the sort of alarm/warning that there are no shortcuts to turning it off.
I am warned by the servicepeople that it will take a while to make sense out of an alarm that goes off with no valid reason. In the meanwhile, an alternate vehicle is needed.

Loaner cars, also known as courtesy cars, are no longer financially practical for this business. Sure, they still have cars of the same make that they sell, cars which in good time will be sold themselves, which are reserved for customers whose cars are in the shop. However, "courtesy" is no longer the word for it. Using a contract with Enterprise rental cars, the dealership rents out its own vehicles to car owners whose cars are being held hostage, I mean being serviced, by the service department.
So I agree to the whole rental deal and the substitute car is put on my credit card, I mean the contract is. This car, thankfully, is no convertible. It does, however, have a moonroof, or sunroof, or whatever one calls it. A feature I don't use. So I leave my auto there, and drive away in this big SUV thing.

Two weeks pass.
Many phone calls back and forth. A couple times I just stop whatever else I'm doing, drive over in the rental substitute car to the service shop at the dealers, and demand in person to know what they can tell me about the car I own.
No, the problem is not the car top. The problem never was the car top. The problem is in the electronic circuits someplace. The servicepeople are going through the connections and the wires by hand. Of course the auto has a computer, but the computer in this case refuses to offer up any helpful code, or any code at all; so the computer has to be, erm, serviced as well.

Believe it or not I have to get off this computer --
so, to be continued.