My Alpine stereo, in my 2001 Continental, works fine except for the two rear bass speakers under the rear parcel shelf. They don't work. Without them, I'm not getting any bass. I took a volt/ohm meter and tested them and there's nothing wrong with the speakers. I replaced the subwoofer amplifier, with one I got from a junk yard, but that didn't help. Do you think it's still the subwoofer amplifier? Any easy way to test it out of the car? Thanks.