Could the cruise control module have something inside it to make the noise. I've never had it apart but it does hook up to the speedometer cable at some point, i think under the hood though. It also has a vacuum switch IIRC plus power running to it.
Not to mention the duct tape that mounts it could have come loose letting it flop around under there? just a thought.
1982 Wagoneer, NP208, D44 Front, AMC 20 Rear, AMC 401, TF727, 4" suspension lift, 35X12.5 BFG MTs