My two White's have shed recently, one yesterday and one today, and both of them made a high pitched squeaking noise beforehand. It worried me when the first one did it yesterday, but then I saw him shedding and thought nothing of it, but then the second one just did it a while ago before he started shedding as well.
But I have never heard it before and I have had these frogs for a little over two years now.
I tried Googling it but nothing came up.