I have Sound Blaster Fatal1ty Platinum sound card and Creative 2.1 speaker set.
For headphones it's usually about 30-40 minutes of gameplay and on speakers it's much longer, sometimes it does not happen at all.
My sound card has 3 modes - Entertainment, Gaming and Audio Creation. After turning the game off, the crackling sound doesn't stop, I need to the card's mode - this seems to "reset" the sound and the crackling stops. Although, as mentioned - sometimes it comes back straight away when I switch the mode back to gaming and then the only solution is to restart my PC.
I read somewhere that Sound Blaster cards haven't got the best compatibility with Skyrim and that lowering the sound quality helps, so I tried lowering it from 24-bit 48000Hz to 16-bit 24000 Hz, but that doesn't seem to help at all.
It's driving me nuts, I've spent long long time sorting out my Skyrim installation (STEP + SkyRe + many other mods) and when I'm finally able to play I get this!
Any suggestions would be greatly appreciated.
P.S.
All my drivers are updated, I have Windows 7 Home. My system: AMD Phenom 2 6-core 3.2 GHz, ASUS GeForce GTX660 2GB VRAM, 4 GB system RAM.