I just bought a house a year ago. In the middle of the night my sinks, and toilet will bubble, (Air Coming out of drains maybe). I will wake up in the middle of the night and I hear the drains. No water has been run all night. Sometimes sediment will come up but not often. I don't detect a smell of anything just the sound is irritating,
I forgot to add. I'm on city water, and drain system.