Did he check the headset/stem? Quite often creaks can come from the headset/stem area & resonate through the frame. On a quil stem you can drop a little gear oil around the top of the headset nut & let it seep in. It doesn't take long to pull a stem & check the headset, either. Handlebars are another culprit. It usually pretty obvious when they are creaking, though. Check the torque on everything.