Losing coolant at manifold heat riser - Why?

When running my new motor, I notice that there is coolant boiling in the little C-shaped hole on one of the heads. Not a lot, but it's worrisome. Can't figure out where the liquid is coming from. Is it possible for it to ooze up through the manifold bolts? There is no coolant in the oil. When I installed the manifold I torqued everything to specs. The heads were milled a smidge just to true them by my machine shop. I used the good Felpro gaskets.