Guinea hens do not really have an "egg song" like chickens. Probably because they don't want the whole world to know where their nest is. My guineas sometimes lay eggs in their coop/run, but I can never catch them in the act.
Do you mean the noise which kind of sounds like "buck-wheat, buck-wheat"? This is what the hens calls most of the day. As other people have mentioned before it is like a "come-back" call for the cocks. If one of my hens is, say, out in the field alone and she's buck-wheating a lot, a cock is likely to come running. The hens will also do this if the cocks are right next to them though. The hens are just chatterboxes.
Now, while the guinea hen is sitting on her nest laying an egg she will call something different(Not necessarily after shes done laying though, generally 5-10 minutes after being on the nest for the first time that day) She will call what sounds somewhat like the alarm, yet slightly different. This is one of the easiest ways to find the hens nest. If you know which hen it is, and who is her mate, simply follow him and he'll probably lead you to or close to the hens nest.
