I've had my 4.1's since 2002 without a problem (knocks on wood) I bought a second set when i saw someone selling the for $50 locally. sure they crackle when you turn the volume up but i rarely mess with the volume knob. both my friends that had the 5.1's have had them die.
Get some tuner cleaner from RadioShack and spray that into the volume knob surrounding space. That should fix the crackling issue. It's caused by oxidization from using lower quality metal for the volume post. My Emu 0404 USB has the same issue on occasion and the tuner cleaner fixes it.