Follow these instructions (seriously...strange as it is)...this works for Blitz 99 and 2K...
Load the game... when the game comes up hold down button 1 or 4 ...I can't remember which...it's the one that makes the screens skip to the next screen in the attract...you can also wait if you'd like, but it takes a lot longer. Once the game comes up with gameplay in attract, THEN coin up and it will let you play.
I don't know why this happens, but it does...
BTW: I only get sound hiccups when the four "shields" come down between gameplay screens and once in a while during "intermissions" in gameplay. I don't think I ever get sound hiccups in gameplay itself.
Make sure you're running MAME 64-bit if you're running a 64 bit OS. I go about a 30% framerate boost going from XP running MAME to XP x64 running MAME 64-bit compile.