We have been experiencing a high pitched whistling noise from the pipe that connects to our upstairs neighbours flat, whenever they run their hot water it sounds like someone is boiling an old fashioned kettle. Unfortunately this goes off all through the night as they all work different shifts. We are unable to establish if this is a problem with the pipe in our flat or if it is coming from their boiler and then vibrating downwards (we can't ask them as they don't answer the door and they don't speak English). This is driving us mad and we haven't been able to sleep. We don't want to call out a plumber if it's their problem. Please help!!!