Do you have speakers plugged in? If you do this is completly normal. On the MBP and the iMac speakers don't plugin all the way causing this noise. rotate the speaker plug and wake it from sleep again. This should solve your problem.
Mine does this, but it's *very* quiet. I'm fairly certain it's just the audio circuitry coming online after being powered down. I suppose it could be considered annoying, but I barely even notice it on the rare occasions I can even hear it.