Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_1 like Mac OS X; en-gb) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8G4 Safari/6533.18.5)
Yes, that's the sudden motion sensor (SMS). It's designed to protect your hard drive if you drop your laptop. The click/scrape noise is the hard drive quickly parking its head. The newer models (2010 and later) are a bit trigger happy when it comes to acivating the SMS, but still it may suggest you are handling your MacBook a bit too rough.