Don't know if this is going to work but this works on Vista with some who have crackle problems.
On sound device properties: Advance: Uncheck exclusive mode that allow applications to take exclusive control of your device.
If you still have issue then try to decrease output level or change the frequency format by configuring the codec driver. Sometimes when audio is overly boosted, the sound quality creates unwanted noise such as crackles.
And what measures have you undertaken?