Risking my ATS reputation here, but your the only ones that might know.

I also know exactly what you're talking about cos I too can make that sound whenever I want. Unlike most things in life however I've never thought about it deeply enough to find the answer. Big thanks for asking though man as it has always intrigued me.

Tell me how long can you actually do it for? I've just tried now and can go for nearly a minute and then it begins to stop and start until I can't do it any more. But as soon as I stop trying and then try again once again it goes for about a minute. And no this isn't a mines bigger than your comp I'm just curious lol. I can't make it loud enough to totally drown out conversation tho

Hmmm... Not sure if i can do what you're talking about, because you say you can hold a conversation. The sound I can make is a rumbling sound in my ear and I have to distort my face quite a bit so it would be noticeable. I can smile really big to the point the muscles near my ear are tensed up, its like smiling with all the upper muscles around your eye, and you don't have to use your mouth muscles, but your lips get pulled up by the other muscles so it looks (im guessing) like a freaky insane clown smile. And my abdomen wouldn't change it I don't think.

Sounds interesting though. I have heard high pitched ringing out of nowhere, mostly as a kid and now it very rarely happens... Also as a kid I remember hearing a deeper sound that kinda reminded me of water moving through pipes... It's a nice topic, especially with all the strange sounds going on lately... Thanks for sharing!