why wont my speakers pick up vocals?

[dodgechick72]

i had aftermarket speakers in the rear deck, 5 by 7's. and for a while they worked. then i got a deck for my car and they still worked fine. but then i put a sub in my car and i didn't touch the speaker wires in the back of the deck. and i got my sub to work fine, but now my rear speakers only pick up the highs and a little bit of the lows. i even unhooked the sub and they do the same thing. they pick up almost no vocals at all. i have adjusted every setting on my deck and they still dont pick up vocals. but when you press hard on the metal near the speakers they turn on. its the weirdest thing. HELP!!!!