Agnosticism of Augustine and Aquinas

In lectures I have often heard the anecdote that Thomas Aquinas and Augustine were in fact agnostics to the (scientific provability of the) existence of God. Okay, it might not be in the traditional sense of the word agnostic, but more of a narrow reading of the term I guess. I really want to use this in a paper I'm currently writing, but I need sources. I've heard some professors mention it a few times, as if it's common knowledge, but somehow I can't seem to find a good quote to back it up. Is it okay for me to ask for help here?

Catholic Philosopher G.K. Chesterton talks about the "agnosticism" of Aquinas in his work St. Thomas Aquinas: The Dumb Ox

See Aquinas's discussion at Summa Theologica I,q.2,a.2 and 3.
http://www.fordham.edu/halsall/source/aquinas3.html

This requires careful reading. I don't think he is agnostic, but his opinion is highly nuanced.

For Augustine, there's a good discussion at the Radical Academy website:
http://www.radicalacademy.com/philaugustine1.htm

See Sections III. Epistemology, and IV. Metaphysics (the first part: Theodicy). It doesn't give any references unfortunately.

I think Augustine is sort of agnostic in the sense you described.