I have an air conditioner that has an in-floor intake. When the heat pump turns on, there is a fairly loud humming that comes from the intake. If I step in certain places around the intake the humming will go away until I move where I am standing. The ducting is in the crawl space under the house and actually where I step to make the humming goes away is in the opposite direction of where the ducting runs by a couple feet.
Does this mean that part of the ducting is loose under the house or something and I just need to find the spot and tighten it down?