Sound works for seconds then quits?

I have an iphone 3gs that when i got the speakers were bad so i replaced it and then the volume mute and power button stopped working so i replaced the ribbon on that and they work fine. but for some reason the sound out of the bottom speakers will sometimes play and then quit. when i plug headphones in there is no sound either when the speakers aint working which makes me think they are related. also i cannot hear any sounds coming out of the ear speaker the one you use when making a call. any ideas?