D.W.
I think it could be a lot of things, too.
Perhaps she's gassy, and her latch isn't good enough that it's creating more gas while nursing (or perhaps it's something in the breastmilk that's creating her stomach to be upset).
My kids both took to nursing really easily, so I never experienced the crying thing except for one isolated incident in the hospital with our second.
Do you pump? If so, you may want to try the breastmilk in a bottle (someone other than you will likely need to try giving it to her) to see if she makes the same sounds when feeding in general.
It never hurts to call the lactation consultant at the hospital or the La Leche league to see if they have any thoughts either.