Generator noise is a predictable source of complaint and it is largely designed out at installation rather than fixed afterwards.
What they actually produce
Manufacturers publish sound levels at a stated distance, usually 23 feet, and separately for the exercise cycle and for full load.
Air-cooled residential units are broadly comparable to a loud conversation or an air conditioner at that distance, and rather more at full load.
Sound falls with distance, roughly by six decibels for each doubling. Moving a unit from 10 feet to 20 feet from a bedroom window is a substantial reduction and it costs a little pipe and cable.
The exercise cycle is the complaint
An outage is an event everybody understands. A generator running for twelve minutes every Tuesday morning is a recurring intrusion, and it is what neighbours actually object to.
Most controllers allow the day and time to be set. Mid-morning on a weekday is the usual sensible choice — not early, not a weekend, not during a nearby household's night shift.
Some allow a shorter or quieter exercise mode, running at low speed without engaging the alternator load. Where available it is worth enabling.
Do not disable the exercise. It is what keeps the machine able to start, and disabling it usually voids the warranty as well.
Placement
Away from bedroom windows — your own and the neighbours'.
Away from the property line where a boundary noise limit applies.
Not in a corner formed by two walls, which reflects sound outward rather than absorbing it.
Exhaust directed away from the house and from adjacent properties.
Every one of these is free at design stage and expensive afterwards.
Enclosures and barriers
Manufacturers offer sound-attenuating enclosures on some models, which help meaningfully.
Do not build your own enclosure. The unit needs a large volume of cooling air and it produces exhaust, and both the clearances and the airflow are part of its listing. A homemade box causes overheating, and a hedge planted too close does the same thing more slowly.
A solid barrier at a distance — a fence line, a garden wall — that does not intrude on the required clearances is the safe version of the idea.
Liquid-cooled units
Quieter than air-cooled at comparable output, and considerably more expensive.
Where noise is the binding constraint — a dense neighbourhood, a strict ordinance — that is the technical answer, and it is a large step in cost.
The rules that may apply
Local noise ordinances, which frequently set a limit at the property line and sometimes different limits by time of day.
Homeowners' association rules, which may restrict placement, require screening, or restrict exercise times.
Both are worth checking before ordering, because they can determine the model as well as the location.
Talking to the neighbours first
A conversation before the installation costs nothing and prevents most disputes.
Telling a neighbour when the exercise cycle will run, and offering to move it if it lands badly, converts a recurring irritation into a known feature — and in a long outage the household with the generator is generally the one everybody else is charging phones at.
During a long outage
A generator running continuously for days is a different experience from a twelve-minute exercise, for everyone within earshot.
Two things help: shedding loads so the engine spends more time at a lower speed where the controller supports variable speed, and simply telling the neighbours how long it is expected to run.
Households that offer a neighbour a place to charge a phone or keep medication cold rarely have a noise complaint afterwards, whatever the decibel reading.