Probably is not the culprit but what are your temps?
You can try Speedfan, link is in my sig, but know that it can throw wrong values from time to time. Just double check with the values reported in your BIOS.
What did you mean by reverting back to system settings? Did you mean Windows Restore?
If you are pretty sure that this started up after an update than I would reformat and reinstall Vista. Unfortunately, Vista doesn't have a repair feature like XP does.
One thing that you can try, before you do anything too drastic, is to create a LiveCD of Linux and run that to see if you have the same issues. If there is crackling when in Linux than it is more than likely a hardware issue, if not than it's your OS.
If you are unfamiliar with a LiveCD, basically you burn an iso image to a CD and than boot to your CD drive and you have a working copy of Linux up and running without touching your Vista installation. Once you are done testing, you remove the CD, reboot and you go back to your original OS.
There are many flavors of Linux out there, my favorite right now is Ubuntu. Here is their download page with instructions on how to do it.
https://help.ubuntu.com/community/LiveCD
Let us know how it goes.
Pauldo