Ok I put in new speakers in the rear a few months back and were working perfectly until last weekend, when I went to crank the volume there was a high pitch squeal. I quickly turned down the volume and it was just fine. But later on it came back on again. Thinking it was the speakers pullled them out and checked them. Speakers pumped really well pretty sure the speakers are good. Even went to Bestbuy to get them to checked out. Even the dude said the speakers were perfectly fine and the cause could be the deck.
So i ended up putting in a new deck since the one I got is pretty old. So got the new deck in and everything and still the problem is there. But now the speakers work but it seems like the sound is staticie and distorted. Thinking it might be connections to the speaker i even changed them and re-solder the wires to the terminal jacks.
It could be your factory amps. I’m not sure what model your car is but i know some/most 240’s have stock clarion amplifiers in them. It’s possible that an after market deck puts out more power then those little amps want to see… you could have cooked one of your amps. Solution… Run speaker wires from your deck directly to your speakers and bypass the stock amps… it will sound better that way anyway!
as a test, you can pull your deck and just run a wire directly to one of the speakers to see if that solves the problem.