BCLK and Spread Spectrum

Hi, I'm new in this forum. I want some help about my ASUS P8H77-M LE motherboard. I told about this to Asus and they were not much of a help. I get slightly distorted audio, from both onboard and external sound cards, most probably related to jitter and/or Spread Spectrum. ASUS AI Suite shows BCLK varying 99.7-99.9, instead of a solid 100 MHz. Unfortunately, my BIOS has no option to disable PCI-E Spread Spectrum. I could really use some help disabling spread spectrum by using a custom BIOS. Thanks for any help.

(Sorry for my bad English)