Birds overhead - cranes?

Can anyone confirm the kinds of birds that I am hearing overhead? I am in Mableton, GA. Which is a suburb NW of Atlanta, GA. Each year, in late October or early November, (the latter this year) flocks of large and loud birds fly south in V formation. Now, February, they are making their return.
Based on this unusual sound they are making, I think they are whooping cranes, but I don't know anything about these birds and am just guessing. Am I correct?
If not, what are they?
And if you can tell me, where is there summer home and where is their winter home.

I'm going to post this on the GA Thread too because I've watched these birds for about 5 years and their calls today have finally prompted me to look into it! Thanks for any help you can give me. ^_^

Hi 3g's, I wouldn't have thought Whooping Cranes as much as Sandhill.

Here is the Whooping Crane sound; is that what you hear?

http://www.birds.cornell.edu/AllAboutBirds/audio/Whooping_Crane.html

Here is the Sandhill.

http://www.birds.cornell.edu/AllAboutBirds/audio/Sandhill_Crane.html

I"m about 99% sure it the Sandhill Crane! What a great resource you and that cornell site are. I would have never gotten to see them. So sound was my only option. Since I'm so far down from them, the pitch is a bit lower, but that gargle sound it just what I'm hearing. When they come through (usually in one day), I'll bet there's a 1000 of them. It is so great to watch them. My whole family looks forward to it. Giant V's that join up... It's great.

Thank you so, so much. :-)