Im having a similar issue with my 24" monitor,
I narrowed it down to the dual link dvi cable, if I connect a no frills DVI cable and set it at 60hz I cant hear any buzzing noise or electrical whine, If I connect a DVI Dual link cable (apologies I dont know the difference between all the different types)
If I connect a dual link cable the monitor will do 120hz yet I can hear buzzing noises when scrolling websites and viewing images or pages with lots of content,
I also found that If I was to google "wallpaper" for example and click on images, full screen that webpage and it will buzz when moving up and down the page, If I narrow the webpage from right to left the buzzing stops when the webpage fills about half the screen, very odd!
Good luck sorting it out mate!