I heard this weird hum in what I would judge as similar frequency band to yours when I stayed at my sisters new house. The thought that I have a weird new ear p

I heard this weird hum in what I would judge as similar frequency band to yours when I stayed at my sisters new house. The thought that I have a weird new ear problem or something really freaked me out at first. And then I realized that I'm only sleeping on a thin mattress directly on the floor and they have a water circulating under floor heating there that just created this hum.