2000 Buick Century Rattling

Got a 2000 Century that has been making a rattling noise from the motor. Oil is checking fine. When the car is started its kinda loud but eased as it's ran. Any help will be appreciated.

Rattling noise? Tap the Cat with a rubber mallet......Catalyst could be broken up inside, causing a rattling noise....

Thank you I will try that.. The car runs good other ran that

When I was doing my Intake gasket I noticed a heat shield on the exhaust manifold had separated causing a rattle. It was behind to left of the coilpack. Put a self tapping screw in it and no noise since.