I was under my desk today searching for a lost screw to my glasses... While searching around my power adaptor, I noted a little bit of a buzz from it. It's low pitched, but audible 2-3 feet (quiet, but audible). When unplugged from my mac, the buzz disappears and becomes a BEEEEEEEEEEEEEEP. Still, only audible from 2-3 feet away or closer. Is this normal, or should I bring my adaptor in for a replacement??? It gets warm as it is (which is normal for an AC adaptor), I just want to make sure my house isn't going to be a smoldering pile of ash some day after work!