I live in a 16 story concrete highrise, on the 10th. Floor. About a week ago, in the ensuite bathroom, I noticed a humming noise, which is getting louder by the day, I can hear in the walk in closet, and also when I go to bed at night now. I've tried putting cushions against the door to muffle the sound, but that doesn't help. I've contacted the strata manager, who said it could be the one of the fans, which are checked quarterly? Anything ideas what this could be?

Ask the strata manager if there's a way to turn it off?