Noise problem

For about a year, my current stereo/speaker setup worked perfectly. About a month ago, it stopped. This is what I have:

My Stereo: JVC KD-S790
http://www.sounddomain.com/sku/JVCKDS790

My Speakers: Roadmaster 5.25" 3-Way
http://www.walmart.com/catalog/product.gsp?product_id=2606838&cat=38981&type=19&dept=3944&path=0%3A3944%3A3947%3A96481%3A38981

Here's the current status: The speakers on the left side of the car sound terrible. Static, scratchy bass, a squealing sound when I turn on the car. The speakers on the right sound perfectly fine--until I turn on the ignition. Then they get scratchy and staticy-sounding as well. All speakers are wired correctly, as is th head unit. I've had alternator whine suggested, but it really doesn't fit the description (high-pitched whine that varies with engine acceleration). I've checked for shorts in the speaker wires (none), and grounding issues (none). The head unit and speakers all are in good working order.

Thanks in advance for any advice, guys!

You blew the speakers... I am surprised they lasted that long.

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No, I did not. In fact, two of the speakers are brand new, as I bought them because I thought that was the problem. Now, if I put them in the left side of the car, they sound bad. If I put them in the right side of the car, they sound perfect when just the power is on, but scratchy when the ignition is started. As I said, the speakers that I have in there now are all in perfect working condition. As an added test, I wired them up to a friend's car and they work great. It isn't a speaker problem.

Only obvious sounding thing would be the headunit then.

Headunit is screwed, I agree. Run new wires... Wires might be bad... I guess you check for shorts, so your only option is new headunit.

check the wiring.. then the head unit

You do need to check the wires. But a problem like this might not be something you can find by check the wires. Disconnect the power and ground from the radio. Run both wires and ground wire directly to the battery. If the nois is still there check speaker wires for a short. If there is no short you are going to most likely need to change the radio. Would not hurt to take a test speaker and hook it directly to the radio either. But I think your problem lies in the power and ground wire.