In order to further reduce vehicle cold-start emissions, the use of catalytic converters that are “close-coupled” to the exhaust manifold is increasing. To understand the vibrational environment of close-coupled and underbody converters, a laboratory study was conducted on several passenger vehicles. Catalytic converter vibration spectra were measured on a chassis dynamometer with the vehicle operating over a variety of test conditions. Vehicle operating conditions included hard accelerations and extended steady-state speeds at distinct throttle positions over zero-percent and four-percent simulated road grades. Some of the conclusions from the study are that: (1) catalytic converter vibration frequency response does not necessarily diminish with increasing frequency through 2,500 Hz, (2) close-coupled converters do not necessarily experience higher vibration levels than underbody converters across vehicle platforms, and (3) underbody converters do experience significantly lower vibration levels than close-coupled converters on the same vehicle.