Raise the car.
Check the reliability of the installation of the fastening brackets.
Use a carrying lamp to check the absence of chafing and burnouts on the muffler.
Check for external damage (dents, scratches). Hit the catalyst with your hand, the ceramic catalyst board is broken when grinding.
Replace severely deformed muffler pipes.
By stretching and bending the rubber suspensions, check that they are not cracked, otherwise replace them.
Check on the assembled exhaust system whether it knocks on the surrounding elements. If this occurs, loosen all bolts, align pipes and retighten bolts.