Whether it is mowers or leaf blowers, none of them should be deafening from over 350ft away.
Professional mowers and leaf blowers need to be equipped with mufflers or other devices to quiet their operation. My honda lawn mower is not even close to producing this much sound even when I'm 10 ft away from it. Residential mowers with smaller engines are obviously much quieter by design. The companies that make the professional lawn mowers must think that they are only used in an industrial park.
The manufactures know that mowers are using these in residential areas and it should be both the manufactures' and the owner's responsibility to ensure they are silenced appropriately.