I just started noticing this yesterday! The sound exists whether or not the stylus is close to the screen, but gets much louder when the stylus gets close. Also, the noise does not seem to exist all the time, for instance, I can't "make it work" right now. The noise is coming from the internal speaker, however.
I have no idea what causes this or, more importantly, how to fix it. I am very interested in getting rid of it though.