Neighbours are oftentimes prone to having disagreements over a wide variety of issues, including noise levels. In regard to operating a lawnmower, neighbours should always be aware of the city and county ordinances that apply. Your City Hall will have a list of noise ordinances that address such issues as when a lawnmower can be used and at what decibel level it can be operated at. If disputes continue, neighbours have the right to take legal action; however, the burden of proof would be on them.
Local counties and cities have the right to create ordinances regarding the times of day in which residents may utilise their lawnmowers, as well as how loud the lawnmower can be. In Los Angeles, for example, residents are prohibited from using their lawnmower before 7:00 am on any given day if the lawnmower is being used in a residential area, or within 500 feet of a residential area. The cities of South Bend and Mishawaka have similar ordinances in place, while other cities prohibit lawnmowers from being used before 9am on weekends. Different cities have different rules and regulations in regards to lawnmowers and when they can be used.
The main issue with residents who mow their lawn early in the morning is not the fact that they're doing the work, but the fact that the work is causing noise. Ordinances have been put in place on city and county levels that dictate how loud a lawnmower can be during the morning hours. In California, the lawnmower's noise cannot be higher than 5 decibels over the ambient noise level. However, the federal government has no power in regards to creating lawnmower laws. As of 1982, the Office of Noise Abatement, part of the Environmental Protection Agency, was terminated by the Reagan administration and, as a result, noise-emission labelling was no longer required on lawnmowers.
Residents who become irritated by a neighbour who is using his lawnmower too early in the morning have the ability to take legal action, as compared to using earplugs and waiting it out. Residents may make their neighbours aware of the city ordinance and, if that doesn't solve the problem, they may sue them in small claims court. The burden of proof would be on the complaining neighbour, who would need to show evidence that the lawnmower was being operated during a non-use hour as well as at a decibel level which is prohibited.