A couple of weeks ago, I was in Elkhart, Indiana and it rained every day I was there. Pulling out, I noticed minor squeek and shuddering when backing (exactly as you describe). After getting out of there and and a couple hundred miles down the road, no squeeks or shuddering. And it just so happens that I'm headed to Gaffney for my 45,000 service which includes a bunch of brake stuff. My suggestion to you is, if you've been sitting still in humid weather, drive it. And it's also quite possible that your 45,000 service will address anything other than glazing.
PS: I'm not a mechanic but I did watch a mechanic fix a whatchamacallit on TV last night. :) Bottom line... I don't think you need a "brake job" on a 2007 DP.