Muffler exploded. Fuel leaking into exhaust? '99 i-30

[freet]

On the highway, the car started to bog down...I accelerated and KABOOM!!! My muffler completely exploded. At the muffler shop they said it was most likely due to a fuel leak into the exhaust. Is this something that has happened to any of you? What causes my fuel to leak into my muffler? How do I go about solving this one? Is it a very expensive fix? They said it will happen again if not fixed. Thanks for your help...great forum*

 

[bossbrakes]

The exhaust pipe runs parallel to the tank, only separated by a heat shield for a length of about 4 feet. Obviously someone needs to take a look at the condition of the heat shield and the tank, to see where the problem lies. But one thing seems strange: when you fill the gas tank to full and there is a leak on the tank, it would have to run out onto the exhaust.......