A8N-SLI Deluxe PSU

Hi,

I'm pretty new to this building a PC from scratch stuff and I put together my first system about 7 months ago.

Here are my specs:
AMD Athlon 64 3800+ @ 2.4 GHZ Cooled with a (Zalman CNPS-7000B Aluminium/Copper version)
4x512mb Kingston Hyper X RAM
ATI Radeon X700 Pro PCI-E
Seagate 300GB SATA HDD
Western Digital 200GB IDE HDD
Sony DRU-810A DVD Recorder
Turtle Beach Montego DDL 7.1 Sound Card
Turtle Beach Video Advantage PCI video capture card
3 LED 80mm case fans
1 LED 120mm case fan
1 92mm case fan
Antec Full Tower Case

I use to power my system with an Antec Neopower 550 but after three months it caused random shutdowns due to low amps on the 5v and 3.3v rails (at the time I only had 4 case fans, 2 DVD Burners, and no soundcard). I replaced it with an Antec Smartpower 2.0 500 watt and it worked without problems until 6 months later. The PSU would work but I could hear a buzzing noise even when the computer was off and the power cord was plugged in. I RMA'd it and got a new one from Antec.

My question is should I continue sticking with my new Smartpower 2.0 500 watt PSU or should I purchase a different one because of the history I had with the original one?

If I should consider gettting a new PSU which one should I get?

I keep everything at Stock speed and do not overclock.

Thanks.