If the landlord's work on the unit that you are renting is actually causing the problems with noise that you are writing about, the loud noise in and of itself would appear to be a breach of the covenant of quiet enjoyment of your rental.I would write the landlord about the situation to see what can be done to rectify the inconvenience that you have had as a result of the improvements being made on the downstairs unit. Keep a copy of the letter for future reference and need. I suggest that the landlord owes you a rental rebate for the inconvenience that you have had to endure.