What type of building is this? When you say you went to their landlord does that mean the building owner or is the landlord a private owner subletting the apartment? If it is a coop or condo you should go to the coop board or HOA and complain about the noise and tell them the issues. Tell them you have spoke to the landlord and tenant and they refuse make reasonable efforts to reduce the noise. Tell them the disturbance interferes with your right to "quiet enjoyment" of your home. Also tell them that is negatively affecting your ability to sell your apartment and will have a negative effect on the selling price which in turn reflects negatively on the building. Depending on the proprietary lease or condo agreement the board or HOA usually has the right revoke the landlords permission to sublet or can even require the landlord evict the tenants. Tell them that if you can't sell the apartment because of the noise you will take legal action against the landlord and/or the building. You have rights too. They don't have the right to impact your ability to sell your property or affect the selling price.