Sand or Sawdust in Exhaust Pipe

[jaxcam02]

So I put on a new catback exhaust last weekend and when we cut the pipe behind the muffler we noticed there was a bit of fine sawdust or sand coating the surface of the pipe behind the muffler. Thought it was weird, anybody have any clue what it could be from. I am hoping its was just in some kind of sand storm on its was to my dealer that found its way into the tailpipe. I have seen absolutely not other evidence of this material anywhere inside or outside of the truck over the last year I've owned it. Will get a picture later today.

[jaxcam02]

Looking at it again it could be something else. Guess I'll try to take a sample and have it analyzed at some point.