problem with sound on jb 3gs

i have a 3gs jb with spirit and unlocked with ultrasn0w runnin 3.1.3...
from time to time i keep havin probs with all the sounds..it keeps goin silent although its on loud mode...i hav to turn off the phone and turn it bak on again..
does anyone know why and what is causing this??

 

wud it have anythin to do wit d fact i hav jailbroken it..coz i hav never faced dis prob earlier before i jb it...