Here's what PeepsCA told me, and it's been confirmed on every professional website I've read.
All guineas, males & females, make the single-syllable "chi chi chi" sound. Only females make the two-syllable, "buck-wheat" call. The most reliable way to get them to make the call (other than many many hours of observing your flock) is to separate them out, one at a time, from the flock so they can't see the others, and wait a few minutes. After a few to several minutes, the females will make the two-syllable call. If you want to know what each call sounds like, just do an internet search "Guinea Fowl Calls" and you'll get tons of examples. Once you've heard it, you'll never forget it.

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I don't know anything or ever read/heard an expert say anything about pelvic bones, so I can't speak to that.
Sexing by wattles or casques is extremely unreliable because the rules for males vs. females is only "in general". Often times it's true, but often times it's not.

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The way to catch a guinea is when they're on the roost at dusk (or night). Free-ranging guineas are really hard to catch obviously - I've never caught a free-ranging guinea because mine are penned/cooped. Cooped guineas are easy to catch at night - take a helper and a flashlight though.

. Once caught, they won't like it.