Mine has the high pitched sound even with the lid closed (screen off) and running an external monitor via the mini display port. I had Dell send me 3 units back in January when I first bought the machine and all 3 of them had the high pitched sound. I thought it might have been the "hard drive" so they sent the 128GB and it didn't solve the problem. I have narrowed it down to an electrical noise associated with a chip on the motherboard. Which chip exactly I do not know. With the covers off you can hear it much better.
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