One of the easiest and most cost-effective solutions for reducing noise is to install a sound blanket to act as an air conditioner noise barrier. You can check with your AC unit's manufacturer for a blanket size that will fit your unit, or you can purchase a universal sound blanket.
Build a box around it lined with foam insulation (nothing on top) about 12'' larger than the hvac unit on all sides, and at least a foot or 2 taller. It will dampen much of the noise and still allow air circulation. You can even build it an inch above ground for more air entry.
Use Sound Blankets and Barrier Walls
One of the most effective solutions for eliminating noise pollution is installing engineered HVAC sound barrier walls. Products like those offered by Sound Fighter Systems are designed specifically for HVAC noise reduction.
The duct silencers enable maintaining proper acoustic parameters in the rooms – even reducing noise in the rooms which require a high degree of acoustic comforts, such as e.g. sleeping rooms or reading rooms. The noise can be generated not only by the flow of air through the ducts.
Upgrade Your HVAC System
Most HVAC systems come with a blower motor that is loud when it's running. This means that you may wish to upgrade your system to a quieter one if you want to reduce the noise from the equipment. You can replace your compressor or add one or two additional compressors.
For the most part, an HVAC system will be very quiet background noise that's easy to ignore. An HVAC system usually won't run loudly unless there's a problem. Your HVAC system, if there's a problem, may make several different noises. You may hear a buzzing noise, a popping sound, or even clanking.
Place Sound Barriers Around the AC Unit
A sound blanket can reduce noise by up to 40%. These blankets wrap around the compressor (typically the loudest component), where the rubber and glass insulation absorbs the noise, trapping it inside the blanket.
The short answer is yes. The blankets are designed to insulate your compressor and prevent the loss of heat. This can also save you money on your energy bill. The blankets also provide a barrier between a hot compressor and any flammable materials that are nearby it.
Find and Replace the Loose Parts
If there is a loose part, such as the belt or bolts, it can cause the blower to shake and howl. Check all belts and replace any that are damaged or worn out. Also, check for loose screws in both fans and vents and tighten them if necessary.
Butterfly Flat Dish Dampers (BFD) – HVAC Dampers
The butterfly flat dish damper is shaped like a circle with two semicircles attached to it. The semicircles are called flaps, and they open and close to direct airflow through a system.
If you hear screeching noises from the outdoor unit when it's running, a bad compressor motor or a faulty outdoor fan motor is the culprit. The fan motor and compression are the most likely culprits of screeching noises from an outdoor AC unit.
Adding new returns or increasing the size of an existing grille is one way to decrease static pressure and help your system move air. It can cut down on noise, too. When possible (and when it makes sense), we can also tie new supply registers into your ductwork or increase the size of existing supply registers.
It is best to place the Duct Silencer within 2 - 4 feet of the blower / ventilator for maximum noise reduction.
Vent silencers are mounted after relief valves to reduce noise pollution to a bearable level. Relief valves are commonly used in i.e. power stations, as well as chemical, petrochemical and other similar plants.
Install an isolation pad or vibration mounts below the unit
Placing the unit on an isolation pad or vibration mounts will absorb those vibrations before they pass into the floor, greatly reducing one of the primary and most disruptive causes of HVAC noise.
If the usual noise volume increases, or you start to hear flapping, rattling or high-pitched sounds from the supply vents, return grilles or ceiling diffusers, it's likely due to an increase in pressure caused by airflow restrictions somewhere in the HVAC system.
If your neighbour's AC keeps making excessive noise even after asking them to do something about it, you may bring the issue to the authorities and local court. It's best to get help from a real estate lawyer.
Steps to soundproof ductwork include changing the structure of the ductwork, lining the interior with sound absorption, creating a soundproof barrier for the exterior, and adding baffles for soundproofing inside the air vents.
The State of California requires that vehicles have an adequately working muffler, which means you cannot remove or make adjustments to your muffler that intentionally increase the noise of the vehicle.