somehiker posted :
"Actually....more like a stick of bombs hitting their target.
Then echoes for quite a while.....like rail cars crossing an iron bridge."
You are right somehiker, the sound is a low rumbling boom, over and over, sometimes lasts only a few minutes, other time for hours. Anyone who has spent much time back off trail in those mountains has heard the booming. Sat up most of one night listening to it, impossible to tell even which direction it comes from. Many explanations I've heard for the booming, volcanic activity underground, dynamite from mining over by Globe, wind along the cliff faces. None make sense or explain the phenomenon.