Is this happening with all sounds?
Is this happening with all your games?
Are sounds actually fully repeating, or doing a sort of stuttered repeat to completion?
(In other words, a little more description would be helpful.)
I've noticed it's pretty common for MAME to choke on games that, as I understand it, are still not very well emulated. NFL Blitz comes immediately to mind. Even on my dual core system, Blitz's announcer takes a good several seconds just to say "Welcome to NFL Blitz!" If it were written out it would look something like
"Wel-el-come-um to-ooh-ooh En-en-n Ef-f El-el-L BLI-IH-ITZ-Z-Z!" (with accompanying stutters in the video.)
Does that approximate what you're experiencing?