Annoying audio click - can you hear it?

I have noticed the following on my XPS 1640:
There's a little click heard from the speakers just before a sound is played. It can be any audio - Windows system sounds, mp3, all of them.

30 second sleep?
Notice that the click is only heard on the first audio played. If you play a new sound shortly after, the click is not there - UNLESS you wait 30 seconds between sounds. It seems the audio engine will go to sleep 30 seconds after the last audio is played. And when it wakes up, it will make this annoying click in the speakers.

Simple way to test this, is to have the Windows volume slider open and adjust the volume just slightly. When you let go of the slider, the system sound is played, but it is introduced by an audible click. Remember to wait 30+ sec between tests. Play around with it. Do you hear this click?

Or is this because I'm running Win7, build 7000?

 

Check your Windows Sound Assignments - it's probably a default sound that alerts you to the beginning of a media file or something similar. Vista's version has a Test feature to play the sound so you can figure out which one it is.