First: Yes, I did see the other thread with almost the exact same name, but his noise would disappear when turning the volume down so I guess it's different.
So, the problem is this... I recently wiped my harddrive clean due to stupid partition problems, and I installed Xubuntu 8.10 yesterday. I downloaded a game, which lagged really bad, which was strange, this laptop being new and all(Acer Aspire 5530). After doing some reading this way and that way I discovered I wasn't using my graphics card at all(ATI Radeon HD3200) due to not having drivers for it. I thought that was stupid, so I went to ATI's homepage and downloaded "ATI Catalyst™ 9.2 Proprietary Linux x86 Display Driver". After a bit of hassle with running the .run file(I'm a newbie) it seemed to install fine, and I rebooted. Then came the annoying sound. It's very high pitched but not very loud. It's not coming from the speakers, i tried turning ALL the sliders down is the volume control with no effect. I can hear it more clearly if I put my ear to the bottom of the computer, not especially clearly with my ear against the speakers.
If I close the lid(So that the display is turned off) the sound stops. Also, whenever the computer is actually doing something, like scrolling, playing a game, anything really, the sound gets all broken up and when playing a game it's almost quiet. The sound doesn't appear until you reach the login-screen at boot. I guess that's all the info I can give. I hope someone knows a solution. I can't sit with this computer in class, it would annoy the hell out of everyone within a five-metre radius...

A guess

There was no problem before you installed the proprietary driver? Do you have the correct driver for the chip on the card (there are two different Nvidia drivers)? What about trying to uninstall what you downloaded from ATI and installing the ATI driver through your Xubuntu repository? I am assuming that there may be some discrepancy between Xubuntus window management and the ATI driver you downloaded. As I said, a guess, but there was no other response. Good Luck

If not that

If there is no change, try a fresh installation and the ATI driver from Xubuntu. Maybe the glitch you said you had the first time caused a problem.