Car Stereos: Car speakers crackle/pop, blown fuses, rear speakers

Question
Hey, thanks for your help. To start off my question, some background info is needed.  It started when my key for my car got stuck in the ignition and could turn to all positions except off.  My aftermarket stereo and aftermarket front and rear speakers still worked fine at this point.  I had to disconnect the battery so it wouldn't be drained.  Had to reconnect the battery the next day to drive my 99 Alero, but now the speakers crackled and popped with greater volume and more power intensive beats.  I swapped my aftermarket deck out with my factory deck and everything worked fine.  I had another aftermarket cd deck that I tried as well, and it too made the speakers crackle/pop.  I checked all three fuse locations for blown fuses, but found none.  The wiring harness from the car to the wiring harness of the aftermarket deck is the only thing that changes when I swap the decks.  I'm wondering if the wiring harness from the car is now bad even though I found no signs of burnt wires.  Can you please help?  Thank you every much.

Answer
Hi Andy,

I apologize for the late response to your question.

Generally, when I run into noise problems like the one you're experiencing, I suspect a problem with a speaker or with speaker wiring.  It's most commonly associated with mis-wired speakers; for example, if you had the left and right speaker outputs mixed (the left positive and right negative connected to one speaker, for example) the results could be what you're describing.  In an Alero, you sometimes have rear speakers with a 4-wire connector; if you tried to wire the new speakers using all four wires, that also could cause the problem.  Often, after-market head units seem to be more sensitive to this type of issue than factory head units.  

The only trouble with these scenarios is that they don't account for the fact that everything worked fine until your battery was disconnected and re-connected.  The battery issue should be completely unrelated to speaker wiring issues.  That makes your problem a little more hazy; but since the symptoms point to a speaker wiring issue, that's where I'd start with the troubleshooting.

First, inspect the wire harness and verify that all the wires are correctly connected: look especially for a mix-up between the white and gray wires.  Also, make sure all of the wires are fully insulated, so that there's no possibility of one speaker wire coming into contact with another.  

The next thing I'd try would be unplugging the deck, then using the resistance function on a multimeter to test the speaker wires.  I'd check for resistance between each speaker wire and the chassis ground wire; there should be infinite resistance in this case.  If you get a reading on any of these, you may have a shorted speaker wire.  Next, I'd check the resistance of each speaker, by measuring between the positive and negative wire of each pair.  You should get resistance readings of 3 ohms or higher for each speaker.  If you find a lower reading, you may have a defective speaker.  Finally, I'd check for continuity between each speaker wire and the other wire pairs: there should be infinite resistance between the left front and right rear speaker wires, for example.

I hope this helps, and apologize again for the delayed response.

Brian