Wikipedia

Another use of the term is to describe an object that gets in the way of performing a task. In that sense, the word was coined by Roger Houcke, who used it to refer to obstructions on exhaust piping that prevent a muffler from fitting.

Who Roger Houcke is, though, I haven't gotten very far yet. Searching his name in quotes retrieves 5 results, all pertaining to schwag (is the guy famous for schwag alone?), including 1 Yahoo! Answers link.