well i have the same problem, and its basically cuz my system isnt fast enough. i have an old sound card as well. but ive found that what does help A LITTLE....is to go into the mame configuration settings file in your main mame folder, and change the sound sample rate to "22050"...thats under "mame CORE sound options" just scroll down till you find it. the number there should be 44100 by default, just change it to the above number and that should fix some games.
but for a more permanent solution, upgrade your pc's processor and ram as well as get a good sound card. you can get a sound blaster audigy gamer off newegg.com for around 60 bucks or so i think. maybe cheaper. but check that out, and it should fix your problems....otherwise just settle for what you have for now...which is what im doing because of lack of money!!!!