Most older games have trouble with some of the sound hardware or sound cards in computers these days. The best suggestion for playing the widest selection of games is to get a soundblaster card, as most older games are fully compatible with soundblaster hardware. Even the newest cards (Audigy, Audigy 2, etc...) emulate the old soundblaster 16 operation.

Other than that, if dark forces has a configuration program that allows you to choose what sound chip you have and IRQ/DMA settings, you might try playing around with those and see if you get any results. I know most soundblaster and compatibles used port 220, IRQ 5, DMA 1...

(I wish I could provide more info, but it's been ages since I played Dark Forces and I can't remember what the sound configuration was like)