I'm no help at all when it comes to being a mechanic, but our Exmark 48"'s with Kawi's do the same thing. (Big Bang and Fire show!) Our mechanic says, besides blowing apart the guts of the muffler, it won't do any harm. He told us piston and rings would do the trick, but ours are 10-15 years old. Yours, much newer, I wouldn't understand. Are your dealers any help or do they fit the description of "the rest of them!!) Be carefull!!<br><p>----------<br>"guido"<br>David M. Famiglietti