While some noises are normal, such as a quiet hum or the sounds of air whooshing through the vents, sometimes HVAC systems make strange noises and can become loud, disruptive annoyances. This doesn’t have to be the case. Check out these common causes of noises in an HVAC system and what you can do about them: Rattling Hearing a rattling noise coming from your HVAC system could mean a few things. If it originates from the outdoor unit, chances are you have some kind of debris