It might be this one. But I think you're talking about the one
that goes suddenly , "WYAHHHHH!" This might be them in a different
state.http://www.learnnc.org/lp/multimedia/3508
A nasal bleat of about 2 seconds is the call of the Sheep Frog (Hypopachus variolosus).Specifically, the voice of the Sheep Frog is similar to that of the Great Plains Narrowmouth Toad (Gastrophryne olivacea), but lower in pitch. The repetition of the call varies, and there can be quite a wait between the nasal bleats. It may be heard between March and September, after heavy rains.