I have just built a system and when I power it up it seems as if something within the CPU or heatsink is rattling. I unplugged the heatsink's fan and it still made the noise. The computer posts and the specs are listed as below:
Athlon II CPU (w/ default heatsink)
Biostar A780L3G mobo
2GBs of DDR3 OCZ RAM
ATi Oxygen GPU
So, it's not the CPU heatsink's fan? (Don't forget to plug it back in!)
Two things to try: unplug your optical drive(s), and see if notice persists (they can sometimes make a hella-ton-a noise, doing who knows what); get something wooden (not metal, so you can't electrocute yourself) and stick it through the PSU's fan grill to stop the fan, to see if that stops the noise.
Nope its not the speaker either... Its not the PSU fan, not the CPU heatsink fan, not the speaker, not anything in the PSU, and its not a drive either.. Very suspicious. I can live with the noise I'm just worried the PC is damaged.
I have the exact same board and the same strange noise. Definitely coming from the motherboard somewhere. I haven't tried loading any OS yet though. So after you boot into your OS the noise goes away and doesn't come back? I read somewhere that some people get noises from the coils or capacitors on the board, but those noises come and go when the computer is running. For me if the noise goes away after the OS boots, then its no big deal, I can live with it.