Or like mine, it went from a hissing to a BLAMO. I just about had a heart attack. I was accelerating, and I was irritated by my exhaust leak. And then suddely I had that 'open header' sort of sound as something gave way. My exhaust back pressure dropped to 0. The truck sounds wicked running a the 310 tune with open exhaust manifolds.
I thought I had a leak in my bellows, but it ended up being the flange that attaches to the right hand exhaust manifold. It broke entirely off. The flange is still attached, but the pipe up pipe is just hanging there.
Looks like a manufacturing defect to me.