A question about exhaust noise...

I don't know how many times this happened during the 15 hours of driving to FL because most of the time I had CDs in and the vol cranked up. In Ga, after making most of the trip at 80 MPH in cruise, I got stuck in heavy traffic and construction dropping me down to 60 or so and doing a lot of accelerating and decelerating. I had the radio on and thought I heard something strange and killed the music. This is when I heard what sounded like a Honda "fart can" muffler sound everytime I pushed down or let up on the gas. It was very loud and "Ricey". This went on for 60 or so miles, then all of a sudden it went back to the normal quiet exhaust tone of the stock Redline.

Any ideas of what could have made the exhaust tone loud and Ricey, then go away? I made the rest of the 150 mile trip and the exhaust noise never returned. This is weird.