Ignoring any mysterious A/C noise can allow minor issues to become major expenses. These noises can signal anything from your air conditioner needing a simple tune-up to the repair or even replacement of the entire unit. The sooner you can determine the cause of the noise and resolve your A/C issues, the better.

Banging Noise.
If your A/C compressor is making a noise that sounds like banging, there is probably a loose or broken part in the compressor. Hearing an outside A/C unit noise like banging usually means that your unit has experienced wear and tear over time, causing compressor parts to come loose and bang or rattle around. The loose or broken part may be a connecting rod, a piston pin, a crankshaft, or support springs and screws. Alternatively, if you hear the banging noise from inside your home, your indoor blower could be unbalanced.
To fix a banging noise from your A/C compressor, you may need to call an HVAC professional to fasten or replace your system’s loose or broken parts. If that doesn’t solve the issue, a full compressor replacement may be required. 

Clanking Noise.
Clanking is another sign of a loose or broken part. If the noise is coming from your inside unit, the parts inside the sealed unit have likely failed. The compressor itself may have become loose, possibly necessitating a replacement. A clanking sound can also mean that the indoor blower or outdoor fan and its blades are out of balance and hitting other parts. 
To fix a clanking noise, you may need to repair your A/C unit’s indoor blower or outdoor fan to set the unit back in balance. It’s always a good idea to call a professional to check out clanking noises before they become bigger problems. 

Clicking Noise.
It’s normal if your A/C is making a clicking noise at the start-up and shutdown of a cooling cycle. However, constant or ongoing clicking is not typical. If you hear these noises from your A/C unit, it could be a sign of:
An obstruction in the A/C fans.
The capacitator loses its charge.
Faulty electrical signals.
A loose A/C fan.
A malfunctioning thermostat.
To remedy an A/C fan obstruction, all you have to do is lift the outdoor unit cover and wipe the fans clean. If your A/C unit is constantly clicking due to the capacitator losing its charge, faulty electrical signals, a loose fan, or a malfunctioning thermostat, you call an HVAC professional to fix the issue. 

Squealing Noise.
Squeaks and squeals transmitted through the duct system suggest a mechanical or air pressure issue, which could be caused by a malfunctioning blower and fan. Outdoor fan motors and indoor blower motors squeal loudly when they’re going bad, and the blower wheel and housing will also squeal when they malfunction. 
Sometimes an A/C unit making a noise like squealing is normal upon start-up. If it’s a sound your unit has always made, it’s probably okay, but if the squealing noise is new, be sure to call a professional to diagnose and repair the issue. 

Humming Noise.
Thankfully, a humming sound coming from your A/C unit generally isn’t serious—but it still signals that something inside your air conditioner is off. Loose parts and refrigerant piping can cause vibration. If left unchecked, you could encounter more serious maintenance issues down the road. 
However, some humming noises may be a sign of electrical problems. If you notice loud humming noises from the outside A/C unit and that the compressor hums and refuses to start, it may be because of loose wiring or a faulty motor. Regular A/C maintenance conducted by qualified professionals can help prevent and repair the root of these electrical concerns.

SOURCE: ahs.com

Ignoring any mysterious A/C noise can allow minor issues to become major expenses. These noises can signal anything from your air conditioner needing a simple tune-up to the repair or even replacement of the entire unit. The sooner you can determine the cause of the noise and resolve your A/C issues, the better.

Banging Noise.
If your A/C compressor is making a noise that sounds like banging, there is probably a loose or broken part in the compressor. Hearing an outside A/C unit noise like banging usually means that your unit has experienced wear and tear over time, causing compressor parts to come loose and bang or rattle around. The loose or broken part may be a connecting rod, a piston pin, a crankshaft, or support springs and screws. Alternatively, if you hear the banging noise from inside your home, your indoor blower could be unbalanced.
To fix a banging noise from your A/C compressor, you may need to call an HVAC professional to fasten or replace your system’s loose or broken parts. If that doesn’t solve the issue, a full compressor replacement may be required. 

Clanking Noise.
Clanking is another sign of a loose or broken part. If the noise is coming from your inside unit, the parts inside the sealed unit have likely failed. The compressor itself may have become loose, possibly necessitating a replacement. A clanking sound can also mean that the indoor blower or outdoor fan and its blades are out of balance and hitting other parts. 
To fix a clanking noise, you may need to repair your A/C unit’s indoor blower or outdoor fan to set the unit back in balance. It’s always a good idea to call a professional to check out clanking noises before they become bigger problems. 

Clicking Noise.
It’s normal if your A/C is making a clicking noise at the start-up and shutdown of a cooling cycle. However, constant or ongoing clicking is not typical. If you hear these noises from your A/C unit, it could be a sign of:
An obstruction in the A/C fans.
The capacitator loses its charge.
Faulty electrical signals.
A loose A/C fan.
A malfunctioning thermostat.
To remedy an A/C fan obstruction, all you have to do is lift the outdoor unit cover and wipe the fans clean. If your A/C unit is constantly clicking due to the capacitator losing its charge, faulty electrical signals, a loose fan, or a malfunctioning thermostat, you call an HVAC professional to fix the issue. 

Squealing Noise.
Squeaks and squeals transmitted through the duct system suggest a mechanical or air pressure issue, which could be caused by a malfunctioning blower and fan. Outdoor fan motors and indoor blower motors squeal loudly when they’re going bad, and the blower wheel and housing will also squeal when they malfunction. 
Sometimes an A/C unit making a noise like squealing is normal upon start-up. If it’s a sound your unit has always made, it’s probably okay, but if the squealing noise is new, be sure to call a professional to diagnose and repair the issue. 

Humming Noise.
Thankfully, a humming sound coming from your A/C unit generally isn’t serious—but it still signals that something inside your air conditioner is off. Loose parts and refrigerant piping can cause vibration. If left unchecked, you could encounter more serious maintenance issues down the road. 
However, some humming noises may be a sign of electrical problems. If you notice loud humming noises from the outside A/C unit and that the compressor hums and refuses to start, it may be because of loose wiring or a faulty motor. Regular A/C maintenance conducted by qualified professionals can help prevent and repair the root of these electrical concerns.

SOURCE: ahs.com