One problem related to loud engine noise has been reported for the 1999 Buick Century. The most recently reported issues are listed below.
While driving at 20 mph the entire vehicle began to jerk backward and forward, at 30 mph the jerking became violent, the engine became noisy and there was a loud noise which appeared to come from below and toward the back of the car. Consumer took vehicle to dealer but dealer was unable to duplicate the problem. Nlm the dealer, not knowing what the cause of the problem is, replaced the main computer. The consumer is upset that the dealer replaced a part on the vehicle that wasn't possibly what was causing the problem.