I went and shook my car all around last night.
No sound when pushing the frame from the outside (thought someone might see & think I was trying to tip the car!).
No sound when pushing on the hatch from the inside or outside.
No sound when pushing the door(s) from the inside or outside.
Then I sat inside, held the door and pushed up and down. Ta-da! Makes sense, as that's where I thought the sound was coming from and the up-down movement (bumps on the road) is what caused it in the first place. So I guess it's coming from either the latch or the weather stripping, as was suggested. My instinct is the latch, dunno why, but I guess I'll try remedies suggested in this and other threads on one, see if it fixes it, then the other if not.
Thanks everyone for posting your ideas/suggestions.