Option B happens to me when I went for a LAN party at my friends house. 2 PC, 1 laptop and a PS3+TV was running at the same time, and I heard crackling at the PC and the laptop. The crackling noise is heard most clearly around the PSU area. After he upgraded the wiring and all it stopped. Even so back before, I haven't had any problem; although I had my worry.
Option A, if your system is what is listed in your signature...I also wonder. Do have any extra PSU you can test the mobo with?