New car speakers still sound horrible?

i just installed new car speakers, kenwood, and the left speakers are fine, but the right ones...i dont want to say they are making a popping sound because that sounds like they are blown, but its almost like they are farting. only the ones on the right side of my car. what exactly could be the problem? i have an 88 chevrolet celebrity. i still have the same stock stereo in there, could that be the problem, in which i can just go buy a new better one tomorrow? or is it a wire problem in which case i would have to take it to a professional and get my car rewired, and how much would something like that be? i would just like some more info on this issue. i dont know much about cars, but installing speakers and a new deck wouldn't be a problem for me, but rewiring is a little out of my knowledge.