What Causes Noisy A/C and Heating Units?

Now that the Halloween season is firmly over, any bumps, bangs, or boos you hear in your home aren’t likely caused by ghosts. But if the culprit of these uncharacteristic noises is your A/C or heating unit, what’s making them happen, and how can you respond?  Loose & Dirty Parts Banging, buzzing, clanking, or clicking …