oh, oh , oh let me guess/ The muffler bearings are failing.Now you have to guess how many fingers I'm holding up. Sorry I'm a automotive ASE technician. Did you follow your scheduled maintenance. Timing belt been replaced. Plugs, wires ect changed every 60k or so. does it have a CEL on. What are the codes, the P420 cat code, multiple missfire codes. PAY someone to do a complete diag on the vehicle or replace parts till they run out of parts or you run out of money. Or better ask people on a gun forum whats wrong with your Shark