Possible causes – Engine mechanical problems– Incorrect timing chain– Stretched timing chain– Failed camshaft actuator or actuator solenoid Tech description There is a factory service bulletin for the following Buick models: 2004-2006 Buick Rendezvous2005-2008 Buick Lacrosse2008 Buick Enclave The service bulletin suggest replacing the primary drive and both secondary drive timing chains. Contact your Buick…