I have this problem and it affects not only videos I run on a second monitor, but even Youtube playback on my main monitor. I can even hear a momentary buzz on bootup, when the chime sounds. I hear the buzz with VCL and with the Windows Media Player and any other way I playback videos with sound.
My son diagnosed this--correctly I think--as a video problem. During each buzz, the video hangs for an instant. He even saw the hangup in my cursor movements, which were not entirely smooth, even when done with great care.
So he found the latest drivers
for my video card (ATI) and downloaded and installed them. He told me that the update would not take effect until I rebooted, which I did. And lo and behold, no buzzing. I thought the new drivers had fixed the problem.
But over the next few days, the buzzing returned. At first, it happened only occasionally, but as time went on, the buzzing rate increased until it hit one buzz every 10 or 15 seconds.
It then occurred to me that what had "cured" my problem was not the new drivers, but the reboot. Ordinarily, I rarely reboot--I can go for weeks without rebooting. Anyhow, I decided to reboot, without any further changes, and lo and behold, no buzzing.
I expect the buzzing to return in a few days, first infrequently, then more frequently, as though something is "building up" in the computer somewhere. But I expect to temporarily vanquish the buzzing by rebooting.
This is not an elegant solution, I know, but it does work, for awhile.