Unity with Sandy Bridge freezes every 5 seconds

I have an Intel Core i3 Sandy Bridge CPU/motherboard, and am running Ubuntu 11.04 Beta 2. I have no problems with Unity on my other laptop (non-Sandy bridge), but on this PC, graphics acceleration in Unity always causes the screen to freeze every 5 or so seconds, for about 2 seconds. It is incredibly annoying that I can't use Unity smoothly.

It happens in:
- YouTube
- 3D built-in screensavers like GLBlur
- The Unity Launcher search box, while typing, it will freeze, then display results
- Basically anything with graphical effects

If I boot into Ubuntu Classic (Gnome), it's fine, no problems whatsoever.

I don't even know where to begin to troubleshoot. The issue even occurs in Live USB mode, so it's not a problem with my installation. It's most likely graphics/Unity related. Everything is up-to-date.