I noticed for me it was during the lobby area mainly when the hard drive was active.  I thought it might be related to a memory conflict between the SATA mobo, my hard drive, and the game memory space it uses.

But that's not it.

Turns out my 3COM NIC card was to blame all along.  I thought that by using a PCI NIC card, it would help speed up my internet connections.  Turns out that's not entirely the case.  Using the integrated NIC on my computer is actually faster because it's designed into the motherboard making digital transfer faster than a PCI slot.

I decided to use my integrated NIC card because it's a 1Gb using newer technology than the older 3COM, and its faster.  When I loaded First Strike, there was no crackling in the sound - it was all crystal clear.  WOO HOO.

SO, if you have crackling sound, and you are using an PCI network interface card, toss it and use the integrated/built in.