Perchance you have an exhaust leak? Give some wear and tear, bouncing around it could be possible.The baffling of the mufflers will have had to deteriorate somehow. If you're taking it off and not use it again, cut into it and see!
2012 SGM Ti DCT Stock and loving it
OEM multispoke 17" with stock rubber summer-15" steel with Michelin X-Ice 2 winter rubber