Another one here. I heard the noise a couple of times the first two days, then nothing for two weeks, today twice. I think there is little point getting a replacement now as it is unlikely Apple has fixed the issue, they are probably just acknowleding it, they need to find a fix, test it and send to production, we are talking about weeks. I am lucky as I bought it in a store that has 90 days return policy, so can wait for a softaware update if it is a software problem, otherwise i ll get a refund towards the end of the 90 days period to make sure the fixes are there.
I contacted Apple support but they were useless, as usual they assume you are dumb, they told me it is a sound setting problem (they told me to turn off keyboard clicks...). Clueless.