had the same problem with my Antec SmartPower 2.0 500w. I bought this PSU because it was a fairly cheap modular power supply. It worked for about 4 months or so then died. I was able to RMA back to newegg and get a new one, which went fairly quick. So in the meantime I used another 500w I had lying around until it got back. On arrival I installed and tested it out, but this time it made an arching sound inside the PSU, that made me a bit worried as it was quite loud too. RMA'ed again, so this time I am on my third Antec SmartPower 2.0, overall would not recommend this PSU.
AMD Athlon X2 4200+
DFI Ultra-D NF4