it's a dosbox sound card setup issue.
maybe use SB16 instead of AWE64(or whatever vs. whatever you're using now), could be conflicting IRQs, or a matter of setting reserve IRQs in the BIOS, etc.
i don't use dosbox, so i can't help resolve the issue other than to point you in the right direction
if nobody answers at this site try here at the dosbox forum: http://vogons.zetafleet.com/index.php?c=7
or you could try one of the ports like eduke32