76 absolutely assumed the noises were Reaper's doing, and though his expression is inscrutable with the mask on, it's clear that he's not exactly buying it, given the fact that he's pretty sure Reaper is just waiting for the right moment to kill him.

Weird robots or not, 76 isn't about to let that happen. Maybe there is something to attack in that room, but Reaper is turning on his heel and marching away, and 76 isn't about to let that happen, either.

After a moment of hesitation, he takes off after him, whether he likes it or not.