Weird humming sound effect not going away

Video here: https://youtu.be/ik8efAk6AJE

It seems like something in the firefight (UESC, heat buildup, consumables, or something else) triggered a humming sound effect to start, but it never ended and continued to play for the remainder of the run.

0:08 Humming sound begins, but hard to distinguish from all the other noises
2:56 Humming sound persists indoors
3:35 Humming sound can be heard clearly with no other noises present