exhaust leak

I think I have an exhaust leak, when I take off, sometimes I hear a rattle, sounds like the cat or something, and the other day I goosed it, and my buddy was behind me and said he could see some smoke coming from under my truck, would I get a CEL for a small leak? my mpg hasn't been great either and Im thinking this may be part of that. so how do I go about finding the leak if there is one?

 

I wouldnt think that smoke would be a sign of an exhaust leak, but what i would do is turn the truck on and crawl under and run your hand over the piping and feel any air blowing.
my brother had a leak once and we found it that way

 

cool, I'll see what I can find, maybe I'll seafoam it and while im at it I'll look underneath.