So, you only hear the noise on deceleration, how about normal accel and hard accel then steady speed at 60MPH? then tell us what you hear when driving steady 60MPH and lightly accel an decel up and down? Drive again and let us know when it happens.
Pretty much during decell at lower speeds but exhaust may be drowning it out. I don't hear it any other times.
Edit....I also tried in reverse but couldn't quite make it out. May still be there but faint if any.