Speakers in my car are sometimes crackly?

I have a 1997 honda prelude with 2 10" subs, 2 300 watt amps, and a 6.5" speaker in both doors. Sometimes the front two speakers will be really crackly sounding as if they are blown, but then sometimes they sound perfect again. Any knowledge as to what could cause this would be nice. I think its something in the wiring, but im not sure where it could be wrong