Please excuse this cross post...
[MY SOLUTION] Same maddening problem with RealTeak hd audio on a new Gigabyte 990FX-UD3 mobo. Not Realtek's fault.
I DID find a solution that actually worked, and I am presenting it below.
I tried newest drivers/uninstalling/reinstalling/reconfiguring/changing settings/updating mobo BIOS... nothing worked.
Here is what DID work -- closing EasyTune.
In initially setting up the mobo after fresh build, I installed drivers and utilities from the mobo maker's disk. One of the utilities on the disk was an app called "EasyTune." It turns out that the EasyTune utility was configured to load at startup. THIS app was causing the crackling. Once I closed EasyTune, the crackling disappeared -- and has been gone for several days now.
If you have EasyTune (or another live mobo tweaking app) running, try closing it and see if that helps.
To prevent EasyTune from loading at startup...
In Win7, go to Start, then type in msconfig in the "Search" field.
Load msconfig and select the "Startup" tab
Scroll down to find an entry called, "ETcall Application" and uncheck it.
Restart
I hope this helps.