VBGamer

I'm playing a midi file using mciSendString and while that is playing I want to put a wave file over the top, using sndPlaySound. This works most of the time, except sometimes when I play the sound I get a loud, screeching noise which continues until I stop the midi file. I checked my midi devce under the multimedia properties and it is using Microsoft GS Wavetable SW Synth. If I change that device to FM Synthesiser, the problem is fixed but the midi files sound terrible (or worse than they usually do). Has anyone ever experienced this problem or know what to do about it?