Do you have a wireless connection? Wireless cards have been known to cause this, as have many other potential problems including your sound card drivers. I do not have a wireless connection and had an Xfi Fatal1ty installed in my Win 7 64 bit system and no crackling or popping (I changed to a different card as the Xfi was interferring with my Sonar recording studio program and nothing to do with popping or crackling).
If you look through the forum you will see many posts on the popping and crackling as users with all types of sound cards/integrated audio have had problems.
Another issue is the video card's drivers - update them to the latest too.