Every few minutes or so, my PSU will start making this rattling sound kind of like a rock bouncing around in a metal can or something like that. The rattling will only last a couple seconds and it's not always the same, but it does this probably every 15 minutes or so. I was thinking that there might be something that's near the fan which would make that sound when it touches the spinning blades. but it seems sort of strange that the sound isn't a constant sound. Anyone have any sort of suggestions short of completely opening up the PSU?