Hmm a few thoughts, Pigeons or boiler?
Just a few ideas...You never know, old houses make a ton of noises, and in my experience, the majority of supernatural phenomena do not create
plain-sensory stimulus.
You wont see, hear, smell, or touch them. They are just there.
Another thought could be raccoons growling.
But then again, perhaps you could be clairaudient.
Or perhaps your parent fancies herself a quick gargle of scope late at night for some unspeakable reason.
I'd investigate for sure.
-GM