When my daughter called the other day she seemed upset. She asked to talk to her dad because she was worried that there was a leak in the walls of her bathroom. She lives in the city in the lower half of a large house. The tenants upstairs were away for the day and she said that there was water running through the walls from the upstairs. She didn’t want to leave her house for work, only to come home to a flooded bathroom. She said that she had called her neighbors and gone up make sure there was no running water,, but the sound had persisted. My husband asked her if the heat was on in the house. She said that she did have it on low and then he asked her what type of heat the building had. She said that they had a boiler that was gas powered. He told her that they needed to contact an HVAC company to have them come and bleed the lines of air. The water sound she was hearing was more than likely caused by the air travelling through the pipes each time the heat kicked on. Boilers don’t require as much maintenance as forced air systems but they should still be serviced occasionally to make sure the water levels are accurate and that the lines are free of trapped air. She said that she would call the landlord and have them schedule the appointment. Hopefully they will do that soon so that the noise will stop making her nervous. At least she doesn’t have to pay for the upkeep of the HVAC system.