My gut says it's a PSU as well (especially since the sound cuts out sometimes, keeps working others). Just because it doesn't overheat doesn't mean it's not failing.
If it's not a huge burden I would try getting a new PSU, even if that PSU isn't the problem, it's more likely than not that someday it will be a problem. (Tom's had a good article a while back about some scary stuff with cheap PSU's)
This is a great PSU if you would like a recommendation: http://www.newegg.com/Product/Product.aspx?Item=N82E16817151095
It's a little pricey for the size, you could probably go cheaper, but be cautious how much cheaper you go because there is a pretty strong relationship between cost and quality.