[IN SHORT] My LCD got some "dizzing...." sound when a particular screen is showed

[Details] My LCD is a COmeMon 17" with DVI, one day, I found that the LCD will emit some dizzing sound( not loud, just little bit, but noticealbe when you are in slient room] when a particular screen is displayed in my LCD.

FOr example, when my browsers is at Gmail Inbox, in which you can see a number of lines with text in your screen, my LCD will have some sound, if I changed the screen by a white blank page, no sound, if I changed the screen by other site,( not a screen with a number of lines with text), no sound....

TEST I HAVE DONE
1. I change DVI to VGA for my 17" LCD, again, same problem
2. I use lower resolution, 1280 down to 1024 --> the sound is less loud, noticeable..less loud.

3. I place my LCD to other machine, at 1024 X 768, no sound emitted? So my display card got problem?

4. NONO, I placed ANOTHER 15" LCD to my original machine in which the 17" was used to connect, no sound emit!

All right, so what's the problem? By using the subsitution method, I cannot sure it's my display card or LCD got problem...or none of them got problem.

PS: I have tried reset the monitor..etc...no use

my COnfig

Asus A8n Vm - CSM New!
Using OnBoard Geforce 6150 display
Antec 430W PSU
2X 512 COnsair DDR 400

any idea? thx