i once spent an entire night thinking that i kept hearing the "ping" sound of the scan, and everytime i closed my eyes i'd see motion hacking circles. i just thought to myself "god, i need tos top playing..." well, that was a year ago...oops. anyway, it turns out i jwas just a dunce and left the computer on the natural selection website witht he music on, and at one point DURING that music it makes a ping sound that was loud enough to hear, while the rest wasn't. i got up the next morning and WOW did i feel stupid, so i played more NS to make me feel better.