Sound Problems

I have an Ensoniq Soundscape Vivo 90 soundcard in a Gateway PentPro200 box running Win98SE. It will play wav files but not mid files. It won’t play mp3’s out of Napster’s internal player but will play them out of WinMedia Player just fine. When it plays windows sounds I hear part of the correct sound surrounded by white noise. The Gateway book on the sound card says that if it will play either one of the sounds but not the other that the problem is internal and has nothing to do with the audio system. I’ve tried switching sound cards and speakers to no avail. Anyone out there have a clue?
Thanks in advance.