Having re-read the whole thread again, as this is a second hand card, you really ought to take off at least the cover and check that the GPU HSF isn't clogged by dust. This can result in a big temperature difference (easily 10C). I would strongly suggest that you do this.

IMO the sound problem is probably something else entirely, but the GPU isn't dust as above then probably the first guy OC'd it too much and damaged the GPU. I don't like the PSU being out of spec, but the regular nature of the crashing makes the video card the likely culprit.