OK - a lot that was unexpected but holy crap, that was good. No spoilers apart from two words.
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Bad Wolf
and two more.
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Cloister bell.
Later edit - from Wikipedia:
Cloister bell
An alarm that tolls, in the manner of a heavy church bell, in the TARDIS to warn the crew of impending disaster. First heard in Logopolis, it rings again in Castrovalva, Resurrection of the Daleks, the 1996 television movie, the 2005 Children in Need special, "The Sound of Drums," "Time Crash" and "Turn Left".
.
.
.
.
.
.
.
Bad Wolf
and two more.
.
.
.
.
.
.
Cloister bell.
Later edit - from Wikipedia:
Cloister bell
An alarm that tolls, in the manner of a heavy church bell, in the TARDIS to warn the crew of impending disaster. First heard in Logopolis, it rings again in Castrovalva, Resurrection of the Daleks, the 1996 television movie, the 2005 Children in Need special, "The Sound of Drums," "Time Crash" and "Turn Left".