Same - blip/click sound from the left speaker area even when on mute. Tends to make the sound just before an alert sound (mail, ichat) but only if it hasn't just made that sound, if you see.
It also makes the noise just after the mac turns on.
However; it's intermittent. It's driving me mad at the moment.
Black MacBook is about a month and a half old.
and no, it's not the hard disc. Failing hard discs make a completely different sound, closer to a ticking watch, this is a single very quiet blip sound.