Not So Super Charger
This bulletin applies to 2013 Cadillac CTS-V equipped with a supercharger. A supercharger noise may be experienced at idle that sounds like marbles rolling around in the supercharger. Some may also describe this as an erratic rattle-type noise that sounds similar to combustion noise on a diesel engine.
This noise will only be heard at idle and it will go away when the rpm is raised off-idle slightly. Typically, the hood will have to be open to hear the noise outside of the vehicle or the vehicle will have to be parked next to a wall to hear it from inside the passenger compartment. This noise may be mistaken for a bad supercharger bearing which may lead to unnecessary supercharger replacement.
If the same noise level has been present since new and it goes away when the rpm is raised slightly, it is most likely a normal noise characteristic of the torsional isolator at idle. If the noise became much more apparent/loud around 18,000 to 25,000 miles, and does not go away when rpm is raised off idle slightly, the internal spring may have worn a groove in the torsional isolator.
Park the car in an open area with the hood and windows closed. With the engine at operating temperature, raise the rpm to 1,200 rpm and re-evaluate the noise while sitting inside the vehicle. If the noise is no longer present, this should be considered a normal noise. Do not replace the supercharger. If the noise is still present, allow the engine to cool.
Temporarily remove the supercharger belt and listen to the noise again. If the noise was present at 1,200 rpm with the belt on but is gone with the belt removed, replace the supercharger and re-evaluate.