Most property rentals have noise clauses written into the leases. A noise violation is any instance in which the noise levels at an apartment exceed what is appropriate as deemed by the lease.
Many landlords consider any excessive and/or late-night noise that's disruptive to neighbors to be noise violations. Most cities and towns have noise ordinances, which are statutes that prohibit sound above a certain noise threshold. If you're in violation of your town or city's noise ordinance, you're almost certainly in violation of your lease's noise violation.
Noise ordinances usually mandate the times, noise levels and types of noise that are allowed or not allowed per the ordinance. If a loud neighbor is bothering you, look up your locality's noise statutes to learn about what is legal or illegal.
Dealing with an extra-noisy neighbor? After taking a deep breath to calm yourself, knock on their door to politely ask them to be quiet. If that doesn't help and you suspect loud neighbors may be in violation of your locality's noise ordinance, you may have grounds to file a complaint with the police.
People may be in violation due to the level of noise they're making or the times of day they're making it. A police officer may use a machine that measures decibel levels to determine whether the noise exceeds legal limits.