The Master caught the strain and it was that more than anything else that triggered him into pulling himself together. Because it was a challenge. If the Doctor could put that much effort into it, he had to at least match that effort.
He took a deep breath, braced himself against the deafening beat and waded into that corner of his mind where the drums stemmed from. Reached out to the Doctor's shining presence and tried to help. Tried to give strength and support, tried to quench the ever-rolling beat, tried to push.