I understand your question to mean that you do not share the same landlord--that your neighbor lives in another property and you want to see what his landlord's responsibility is to the neighbors: the answer is none. A landlord is not vicariously liable for the acts of his tenant. This is why some people prefer to live in HOAs, because in associations, the landlord will be fined by the Board for every violation of his renter--but that has no application here if you don't both live in the same HOA.
You can call the non-emergency number of your local police department and see if what he is doing is against any codes. If so, they an cite him, and you can sue him in small claims court for Nuisance and Interference with the Right to Quiet Enjoyment. If it is not illegal, your civil suit will likely not be successful. You can have a local lawyer send him a cease and desist letter, and see if that gets his attention. But he's not obligated to comply. But the landlord has no liability.
If I misunderstood and you share the landlord, then take your lease to a local landlord/tenant attorney and have him advise you on breaking the lease and negotiating with the landlord.
We do not have an attorney-client relationship. I am not your lawyer. The statements I have made do not constitute legal advice. Any statements I have made are based upon the very limited facts you have presented, and under the premise that you will consult with a local attorney. This is not an attempt to solicit business. This disclaimer is in addition to any disclaimers that this website has made. I am only licensed in California.
Quiet Enjoyment, believe it or not, has NOTHING to due with peace and quiet. Quiet Enjoyment is a concept by which a landlord becomes obligated to assure the peaceful tenancy of his or her tenants and to defend that tenancy against competing claims of title.
A proper response would require a thorough investigation into the history and background of this relationship. The information provided above is just that, information, to be used as you see fit.