X301 sound card buzzing

[force]

Has anyone noticed that the soundcard creates a rattling/buzzing sound? It's not the normal static noise in the background due to electrical noise.

It's noticeable when adjusting the volume in Windows XP's volume control (where it makes the chime) with arrow keys. It sounds like the speakers are rattling or the diaphragm is buzzing against something, but it happens even with a few different pairs of headphones. It almost sounds like the sound is getting clipped, which doesn't make sense since the volume is under '1' on the Thinkpad OSD, or slightly above the first mark on the Windows volume meter.

I've also noticed that turning on/off night mode affects the buzz, but night mode seems to only affect the volume. Since night mode is a soundcard level setting, and that the buzz is reproducible with both speakers and headphones, I'm inclined to believe the culprit is the sound card.

Anyone have any insight?