When inspecting the trailing edge area on the 737 NG, pay attention to the aft lower panel between the pylon and the inboard flapfairing. The attachment strip (waved shape) on the upper side of this panel can have cracks causing a loose panel at the fwd side. You can find it easily by pushing the panel upwards. When this is possible, the attachment strip is probably cracked/loose around the attachment rivets. See pictures for clarification. SeeĀ IPC 57-50-00-30