How I saved interview audio when the room had HVAC noise

In my day-to-day, I handle corporate video production with a tight schedule and non-ideal locations. The problem that stopped me in my tracks was this: the HVAC was generating constant noise right during an important interview. The symptom that made me investigate it seriously was that the image was fine, but the lavalier was capturing a low hum throughout the entire dialogue. I preferred not to…