"Bumping" Sound in Minecart

When riding a minecart, sometimes it will start to make a "bumping" or "jolting" sound. Here is a video of what I mean: http://www.youtube.com/watch?v=tpeEVR81Jas&feature=plcp

(OR if you don't trust links, just go to the youtube search and search this exactly without quotes: "Minecraft 1.4.3 Pre-Release Minecart Bug!"

My music was at 7%, and my sound was at 100%.