I too own this same PSU. and it has the same problem. infact, I've used it for many years. it even had the same problem from being about a couple months old. I ALWAYS thought it was the fan, until I recently stopped the fan by poking a plastic rod in there. I was amazed when the noise continued. it sounds just like a fan rattling. but there is no mechanical explanation left. so therefore it sounds like a [B]cattle prod [/B]in retrospect.

I daren't open the PSU, so the reliable way to stop it from doing this seems to be to switch the PC off, then manually switch off the 0/l switch...