external keyboard causing an annoying repeated error sound

Not long ago, I bought an external keyboard (the standard apple one), so I could raise my macbook pro up off the desk and not kill my neck. I love the keyboard, but not long after I started using it, a very mysterious and annoying problem began. Once in a while when I'm not using the computer at all, the error sound (a kind of middle pitched beep, more like an electronic drum sound) goes off repeatedly. It only stops when I hit any key on the keyboard (external or laptop one seem to both work). Sometimes, this happens over and over again, and sometimes it happens only once in three days. So I'm thinking I won't have any luck taking into the apple store where I bought it, cause the chances it will happen there just for them seem slim.

The problem completely goes away when I disconnect the keyboard. I have trying using different usb ports (I usually plug it into a hub), but the problem occurs no matter where its plugged in. I've also tried closing down certain apps that I were running at the time the problem occured, but it still happens.

Any idea what could be causing it?