I've been having problems with secondlife sound crackling, and being very distorted while using other applications. after a lot of fannying around, i ofund the cause to be somewhat perculiar.
For example;
SecondLife + Teamspeak = Sound is fine (For a while at least)
SecondLife + Winamp = Sound crackles. Extremely distorted until PC gives BSOD or reboots.
SecondLife + Teamspeak + FireFox = Sound is ok, for a while, deteriorates.
The funny thing is, after trying alot of things, nothing worked until I opened up the teamspeak settings and changed the Sound Driver to Direct Sound instead of Wave.
I don't know the exact cause of the problem, and this fix wont work for everyone, but since I did that, secondlife has been running fine with any application.
Hope this can help at least someone. Maybe if some Linden would read it and perhaps look into the initial problem.
Currently I use a "Sound Blaster Live! 24-bit" sound card and an ASRock "K8NF6G-VSTA" mnotherboard.
If theres any other way to fix this issue please let me know.