http://www.pendleton.usmc.mil

[temeculaguy]

http://www.pendleton.usmc.mil/coNoiseLetter.asp

Here is the apology from the commander and about halfway through it confirms that low lying clouds in winter cause the noise to travel further.

In 20 years here I’ve noticed it only a handful of times. I’ve probably heard the 4th of july fireworks more often.

Now you want a consiracy theory, read this one about an unexplained boom in s.d. a few years ago.
http://www.signonsandiego.com/news/northcounty/20060423-9999-1n23bigboom.html