R.A.B.!!!!
REGULUS BLACK!!!!!!!!!!!
ALSO:
From HP & the OotP Chapter 6: The Noble and Most Ancient House of Black, pg 116 U.S. version:
"They foun dan unpleasant-looking silver instrument, something like a many-legged pair of tweezers, which scuttled up Harry's arm like a spider when he picked it up, and attempted to puncture his skin; Sirius seized it and smashed it with a heavy book entitled Nature's Nobility: A Wizarding Genealogy. There was a musical box that emitted a sinister, twinkling tune when wound, and they all found themselves becoming curiously weak and sleepy until Ginny had the sense to slam the lid shut; also a heavy locket that none of them could open...."
The locket is in Grimmauld place!!!!!
More on my thoughts later.