So far, suspending to ram and waking up from it works. My laptop's external display (connected via HDMI) works, too.
However, what doesn't work is the sound, which works before suspending, of course. I'm using my external monitor's speakers and have made the corresponding settings in Ubuntu's sound menu (switched to "Digital Stereo (HDMI) Output + Analog Stereo Input" in "Hardware" tab).
What can I do to fix it?
Edit: when I ran ubuntu-bug, it tested sound output with and without using pulse. Without pulse, it worked, however I still heard the noise. With pulse it was only noise.
Edit: works fine with natty and oneiric now. Updating to latest Ubuntu solves the problem.