An air conditioner is a valuable necessity in keeping the summer heat under control. However, if your unit starts creating unnecessary noises that weren't present before, then you may have a problem. That's one of the many ways these units show something isn't right. Think of it as a headache to a human that may indicate an underlying condition such as being tired, under tension or something much worse.
A noisy A/C needs to be looked into so as to avoid any conditions from worsening. If you're a DIYer, then here are some common cures you can try out.
Check the fan
One of the most common problems that lead to noise is a faulty fan in the condenser. This is a problem that mainly affects the direct drive motors that don't have a belt (most new A/C models).
For starters, check the fan unit. It needs to be clean and properly kept. A harsh humming or rattling noise from the fan is normally a sign of accumulated dust and dirt. The blades of the fan may also be loose, thus causing all the noise. You'll have to tighten the screw using a screwdriver.
Also, check the bearings on the fan if all else is well. However, replacing them needs a professional as it is very easy to further increase the damage on the unit.
If your A/C is producing a loud hissing sound, then you're probably looking at a refrigerant leak problem. A bubbling sound is also a common noise produced when there are lesser severe leaks. Air bubbles penetrate the unit and travel across the line.
To find the source of the refrigerant, search for any discolouration at the HVAC piping system, coils or fittings. These leaks can occur due to a number of causes such as corroded coils or mechanically damaged lines.
After getting the source of the leak, you'll be in a much better position to get a solution for it. Damaged fittings can easily be replaced, and soldering can be used to fix leaking connections. However, if the leak occurs at the coils, then you'll have to replace the whole coil.
High pressures in the compressor
In other cases, very high pressures lead to a 'screaming sound.' A/Cs normally have a sensor to shut down the system when the pressures exceed normal. If the system doesn't auto shut itself down, then the high-pressure sensors are faulty. This is a very dangerous condition, and you need to shut the system down and immediately call a professional.