it sounds like an exhaust leak but everything is tight and i can't find a leak. i suspect that a resonatoris bad. can i use the boat 1 more time before replacing?

Its very easy to remove the riser on a 496. If you are getting a rattle or vibration from one exhaust I would open it up a check things out. the problem could cause more damage that could risk the risers integrity as far a sealing from cooling raw water, and a leak there would be casistrohic. If its just a broken out internal flapper thats not as serious and could be run that way for a long time without damage. If Things are breaking up in the riser find out now not later. Just my thoughts.

Ray @ Raylar