I don’t agree very often with Helene Harrison but indeed, you have to hear the boom she is talking about to get the shivers up the spine that it evokes.
It sounds like an underground nuclear test must sound like: it is a lot like a construction site blast but way, way bigger and a lot farther away. It may be a quarry blast somewhere; it’s not a sonic boom.
It is very unnerving and spooky to hear and I can well understand Helene’s concern.
Anyone who has hear it will attest to its strangeness. Anyone who hasn’t heard it will simply brush it off as “probably exaggerated.” Believe me, no exaggeration is needed. I was severely spooked when I hear it, and I only even heard it once early in the morning.
Hope you discover what it is Helene.