Well the guys there just wrote up a piece on the Castle Thunder Noise, and it's a great write up. They even included a link to a wav file of Castle Thunder, but I made mine louder (Snarky!):
Now go read the write up at IO9, if you're in any way interested in classic movie sounds or sound design, and for more info you can also check out the wiki on CT. someaudioguy some audio guy sound design sound effects voice over voice acting io9 history film
It is surprising how often it creeps up, but it seems to be a staple of movie making (or at least ADR), especially for how long this little sound effect has been around. From Wiki:
The Wilhelm scream is a stock sound effect first used in 1951 for the movie Distant Drums. Actor-singer Sheb Wooley is considered to be the most likely voice actor for the scream, having appeared on a memo as a voice extra for the movie. The Wilhelm scream has been featured in many movies and television programs since. Alongside a certain recording of the cry of the Red-tailed Hawk, the "Universal telephone ring"[1], the Goofy holler and "Castle thunder," it is probably one of the best-known cinematic sound clichés.
Finding this Youtube clip was a joy. Funny just how many modern films/TV shows are still employing it today (though it gets kinda grating when you hear it back to back to back).
SO, check the clip out, and you'll never be able to see a film again without picking up on a scream that's been used for over 50 years!