having problems with speaker sound

I have a sony 1200w amp hooked to sony 6.5" 4-ways in the doors, and an mtx amp powering 2 sony 12" woofers.  All was working just fine for quite some time (1-2 yrs+), when suddenly, the door speakers became twiney, sounded like nothing but tweeters playing (no bass).  I ran some tests on my Alpine deck and the amps.  The deck on both Rear and SubW pre-outs seem to work just fine delivering to the woofers... but when routed to the speaker amp, nothing but tweeter playing... checked the amps the same way, and both amps - speakers twiney... subwoofers work perfectly fine.  Im wondering what other possibilities there could be causing such an issue.  My first thought was that a speaker magnet came in contact with the door or one of the wires leading to the speaker terminals did the same, and if so, could this cause such a problem, even if, for instance, the speaker that was touching the door was disconnected from the rest of the system?  I could be wrong, but i would like to see what other people have for advice and input on solving this problem.  Any help would be greatly appreciated. Thank You :)

I would say that the best way to try and diagnose this is to bench test the speakers themselves. if they sound fine outside of the car then you can work your way back to the amp, first checking the mounting, then the wiring, then etc. also when you have the speaker out if it sounds fine then try putting in another test speaker into the door to see if it has the same problems. there are many options but I would first just pull the speakers and bench test them.

Easy way would be to put a test speaker on your amp. If it plays full range the woofers on your Sony 4 ways are cooked. If it was a wiring issue nothing would play. If the test speaker only plays highs, something is wrong with your amp. The deck cannot eliminate mid range on it's own and just play bass and treble.There is no such thing as free installation!