I'm in my mid 60's and have had severe ringing in both my ears since being a teenager. About 15 years ago I started having sounds like you spoke of as well but only while laying down. At times they sound like gunshots and have woken me out of a sound sleep. One doctor said it was probably related to high blood pressure as was the ringing but I'm sure I didn't have high BP when I was a kid so I think he just brushed my complaint off since I have no insurance to do any serious testing.
I've also been told it has to do with stress and started keeping a log of when the 'explosions' inside my head in relativity to what is going on in my life but to date have found no real pattern.
Good luck in finding a doctor who will help, I've been looking for answers on this subject for years and haven't found someone who has an answer yet.