User blog comment:GothGirlXenon/Uncensored Canadian Version of TD and Alternate Endings Released in America/@comment-13261419-20150702205736/@comment-24400056-20150703070814

It was in the first aftermath at the end of the episode. The sound was heard when the lights were turned off.

Based on the sound, it was assumed they were doing "it" by a lot of viewers on youtube.