At least I think it's John Young. He identifies himself as CAPCOM on the loop. Although the CAPCOM on shift is Vance Brand, there would frequently be multiple astronauts congregated around the CAPCOM console during particularly pivotal moments in the flight. Someone who is more familiar with voices on the loops can correct me.
In "Apollo: Race To The Moon" Kranz would identify this as one of the most contentious moments during the flight, where he was pulled in three different directions by Slayton, Kraft and Faget, as far as how to configure the spacecraft and crew immediately after the PC+2 burn. Because Kranz took Faget's route and opted to use a LM PTC procedure which had never been tested, he started taking a lot of heat from the other Apollo senior management and astronauts when the procedure started taking too long for the exhausted crew to implement.
Link:
https://apolloinrealtime.org/13/?t=081:02:35&ch=8Edit: In retrospect, it's possible that the voice could be Dave Scott since Kranz mentions earlier on the flight loop that he's present in the MOCR and providing input.