I have a thermaltake 480W PSU. When my PC is switched off but still with power cable attached to the PSU, I can hear what i can only describe as a buzzing noise coming straight from the PSU, the same sound you would hear from powerlines if you were to stand right under them. It is loud enough to hear from a couple of meters away. I cant remeber it always doin this so im not sure if its normal or not. Can someone comment.