Your HVAC just started making a noise it didn't used to make. Different sounds mean different problems – some urgent, some not.
You probably came here because…
- Loud bang when the system starts or stops
- Squealing or screeching that lasts the whole run
- Grinding, rattling, or metal-on-metal
- Hissing or bubbling sounds near copper lines or the outdoor unit
What’s actually happening
Bang at startup: usually delayed gas ignition (gas builds up, then ignites in a small explosion) or expanding ductwork. Delayed ignition needs immediate attention – can crack the heat exchanger.
Squealing: worn blower motor bearings or a slipping belt (if you have an older belt-drive blower). Not urgent but the motor is on its way out.
Grinding or metal-on-metal: bad blower motor bearings, dead compressor motor, or a fan blade hitting something. Shut it off – continued running destroys the part faster.
Hissing or bubbling: refrigerant leak. Refrigerant is a closed loop and shouldn't leak. If you're hearing this and losing cooling capacity, call.
What we do about it
Identify the source
Is the noise from the indoor unit (in the closet, basement, or attic)? The outdoor unit? The ductwork? That narrows the diagnosis immediately.
Note when it happens
Startup only? Constant? Only when the compressor kicks in? Only in heat mode? Details matter for diagnosis – jot them down before you call a tech.
Change the filter and check for debris
Something obvious first: is the outdoor unit fan blade hitting a stick or leaf? Is a return grille rattling because a filter is loose? Rule out easy stuff before assuming a big repair.
When to just call
Grinding, metal-on-metal, and delayed ignition bangs are urgent – shut the system off and call (423) 637-1846. Running through those noises turns a $300 repair into a $2,000 one. Squeals and rattles can usually wait a couple days but don't put it off forever.
Ready to fix it?
Call the family that’s been doing this in the Sequatchie Valley since 1996.