JBL, Polk, Sony, Pioneer, RCA, BOSE, Yamaha, and a few others do not make good speakers. Any good speakers they have, they bought from other companies.
I wish you would have bought some nice british stuff, like B&W, Thiels. Some like Paradigm, etc.
From my understanding of these speakers is that they require a good amp. So I would expect that may be your problem.
You may have blown a speaker, probably due to a poor signal. I would take each cone out, and try to play a signal through each cone... No Noise = Dead speaker... Take it to a dealer and see if you can get a new one.
Or just take the whole speakers to someone who deals with Audio and Video (ONLY) and that also can listen to them... Call ahead of time, they usually want a heads up before you start pulling speakers out of your car.
These people are usually more then willing to help you out, and they can put the system on an amazing Amp and Receiver.
Mike