Re: 7X13 The Name Of The Doctor(Grading/Discussion)(SPOILERS!)
I ret-con it as something that has always been there in a more subdued manner. The sound he heard when there was silence, a reminder of whatever he saw in the void and causing his more subtle and creeping insanity. When the Time Lords brought him back for the war, they brought him back 'wrong' and the drumming was now the ever-present and maddening sound he describes it as. By the time we meet Simm's Master it had been pounding in his mind for so long that he forgot a time when it wasn't.
"There is no reason why good cannot triumph as often as evil. The triumph of anything is a matter of organization. If there are such things as angels, I hope that they are organized along the lines of the Maffia." - Winston Niles Rumfoord.