In single-family houses, the air conditioner compressor can be a problem for you or for your neighbors, depending on where you place it. If it is your machine, your windows will be closed when it is running, so it has to vibrate a lot before it will get on most people’s nerves.
Where houses are fairly close together, the next door neighbors may need to close up because of the racket caused by your condenser. That doesn’t lead to neighborly relations in the heat of the summer.
For buyers: When house hunting, look for air conditioner condensers. If you are looking at a first floor unit, you may find your upstairs-neighbor’s condenser under your bedroom window or next to your patio.
For owners: I had a client who had a fairly major confrontation with his neighbors over the condenser. Next door, there lived a child who was sensitive to vibrational noise. The machine was interfering with her sleep. Her mother promptly went to war (as mothers will do to defend their children). My client felt like a heel for causing a problem for a young child, but how can a house get air conditioning without making a bit of noise? It ended up involving the town officials. He ended up spending a good bit to reduce the noise.
This was about ten years ago. Now, there are better ways to get quiet air conditioning.
According to Acoustical Surfaces Blog, getting the compressor balanced helps. If that does not stop the vibration, then shock absorbers like this or this could help. These can be used under the compressor or under the HVAC unit inside that circulates the air.
There are compressor covers now that help reduce vibrational noise (which is worse than the whirring alone). Also, some companies are making quieter units, both HVAC units for inside and compressors for outside.
There is also air conditioner noise from window and wall units. The EPA recommends this:
When comparing air conditioners, check the sound power level label on the unit or in the printed specifications. The smaller the number of dB(A), the quieter the air conditioner. Comparing labels on units of the same capacity allows you to choose a quieter unit…
Also, where you put the system matters to your neighbors:
The siting of the air conditioner is the most important factor in ensuring that noise is not going to be intrusive. Placing the unit at the side of your house close to the neighbor’s house is likely to create excessive noise, as the noise is trapped and reflected between the walls and eaves of the two houses. A fence has limited value in reducing the noise in this situation, unless it is solid and is as high as the eaves of one or both houses.
Placing the air conditioner on the rear wall facing the backyard, or on a front or sidewall facing the street, reduces the noise reaching neighbors. Also, if the noise is found to be excessive, it is a simple task to construct a barrier to shield the neighboring property from the noise.
If a suitable position at the back is difficult to find because of a very small yard, a split-system compressor can often be located at the front, away from the house wall. This option can overcome the inability to use the front wall because of picture windows or pathways. The unit can be concealed by vegetation or a low L-shaped barrier. Modern “split system” condensers are quieter than standard central air conditioning condensers, but they also make noise that can bother a neighbor.
There is a psychological term for people who over-react (in fear) to noises: ligyrophobia. But you don’t have to be traumatized to be annoyed by the buzzing and whirring of your neighbor’s air conditioner, be it the condenser or the window unit. Have you had this problem?