Crackling Sound With Macosx, G5 dual Audio problem apon start up Options

[Mac-Dee]

hey Guros

i have a problem when i restart my mac or load up and want to play audio it clicks and cuts in and out like somethings wronge with the signal ... i'm not sure what it is i use the optical digital out ---then to presonus/monitering central station then to my genelecs
the signal is terriable then fixes itself after about 10-20 mins fully.

I have done a disk scan ... and repair .......i had the problem before and reinstalled i don't wanna have to do all that again... i had all the sleep modes off like disk switch off norton disabled all that but i don't know what the problem is anyone know ?