Fps raising in more then 100% without sound. (sound auto shut down)

hello,yesterday i was playing enemy territory..with my clanmates we were talking on ventrilo,all goes ok with normal fps but little hard to play (60-70) sometimes 100 but NO more.
then my whole sound system stopped working,(ventrilo,game) everything sound just stopped working. but at the moment it happend i saw that my fps raised to 125(maxfps is set to 125) Everywhere!!! when i made it unlimited i had 250-300 and its not only in et, then i tried GTA:San Andreas and game just worked smooth as hell...
but after restart i got sound and again bad fps..

my pc specs are:
intel p4 1600mhz overcloked to 1800mhz
nvidia Gforce fx 5500 128mb
384RAM ddr 266
mboard: epox 4pda
so my question is: why when sound is AUTO shut down i have so much better fps?