silence
There is no silence in the TARDIS. Where there is machinery, there is noise; where there is no machinery, there is still the consciousness of the TARDIS itself, the burning core of energy that lies behind the console, that threads through the walls, and that will not leave him in peace. However fast he runs to escape his ghosts, they keep pace with him and whisper his name.
Even in the Zero Room, he hears the double pulse of a Gallifreyan heart.
Human voices can drown that for a little while. Human babbling, human lives, are his silence, his salvation.
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