Lately my PowerBook has been making a noise that sounds like a cell phone vibrating, although much louder. This happens whenever I shift the PowerBook on my lap or rest my hands on the casing to type. It sounds like it's coming from the SuperDrive, although that's not a certainty. The PB has recently had a logic board, outer case and Bluetooth assembly replacement, but the sound was not immediately present after the computer returned from the repairs. The SMART status is listed as Verified. It's a 15" PB Rev. B running 10.4.2. Any ideas?