^ Seems to be an issue confined to Tucson Hybrid vehicles built for the U.S. market only - vehicles built for the Canadian market (for example) have a much softer, much more agreeable Reverse sound.
The sound apparently comes out of a speaker mounted somewhere in the front of the vehicle. I wonder if you can solve the problem by installing the Canadian version of the latest software update? It might be worth a try. Or try finding the noise maker and put a sock in it!