If you get desperate enough on this issue a few more ideas that could help:
Chassis Ears - for around $50-$100 you can set yourself up to listen for sounds, 5 or 6 points at a time, beneath the 80 as you drive. You could clip the listeners/inputs onto different components until you find the source of the noise.
Mount a camera (like a gopro) at different points beneath the 80, ideally with a mic. and then drive/replicate the sound. Visuals may or may not help here but if the camera had an active mic the noise seems loud enough for it to be picked up and a camera may help isolate the location of the sound (it will be louder when the camera is closer) and possibly connect the sound to specific movement in the drivetrain/suspension.
I really want to invest in a set of Chassis ear and that ebay link sounded good until I saw the shipping cost was about the same as the asking price!!!
