So Sutekth the Destroyer and The Beast have a very similar voice. The Doctor ponders all these images of Satanic entities looking similar, that they perhaps come from one focal point of influence. Possibly this includes the voice, but I have decided that its because the TARDIS translation circuits have a huge but limited number of voices to give to the people the Doctor meets. Thus, the voices of Sutekh and the Beast are modelled on a Gallifreyan super shit from the Dark Times, one who was massively into the Death Zone and may have Runcibled over a few commentaries. His voice print will be kicking about in the Matrix somewhere, and the TARDIS defaults to him whenever it encounters some huge bassy looking radge.
This does rely on the Beast only being able to communicate once the TARDIS arrives, meaning the Doctor has yet again killed people by virtue of just turning up.
Just thought I'd share that.