[closure]

I too can make a rumbling sound at will since I was a child.

What is responsible for this?

I don't know how I discovered how to do this but it always seemed natural.

[maaaats]

Sounds like voluntary opening of the eustachian tubes, also called BTV in freediving. See https://en.m.wikipedia.org/wiki/Ear_clearing

[szemet]

Oh, Thanks. When I was a child I asked all the adults around about this, but they looked at me like I were a lunatic, so eventually I just stopped talking about it.... :) Glad to have an answer now.

[LordKano]

I learned to do this as a child because I always had issues with feelings of pressure in my ears. I was so sensitive that riding up or down a hill that was big enough would cause discomfort.