Music by Kevin MacLeod. Available under the Creative Commons Attribution 3.0 Unported license. Download link: https://incompetech.com/music/royalty-free/index.html?isrc=USUAN1100654

MacLeod's description:

Genre: Soundtrack
Length: 0:54
Instruments: Synths, Bells, Piano, Percussion, Orchestre

Simple drone followed by a crescendo leading to silence.
ISRC: US-UAN-11-00654
Dark, Mysterious, Unnerving 2009