Topic already beaten to death, but just saw this posted:
http://sandyblogs.com/techlink/?p=3690
Supercharger Rattle Sound
September 18, 2014
On some 2014 CTS-V and Camaro models equipped with the 6.2L engine (RPO LSA),
and some 2009-2013 CTS-V and Camaro models equipped with the 6.2L engine (RPO LSA)
that have had a service replacement supercharger installed after November 2013,
a flutter or buzz sound may occur at 800-900 rpm (low rpm) with the vehicle in 2nd or 3rd gear (high load).
The sound may be mistaken as clutch chatter or a heat shield buzzing noise.
The supercharger now has a solid coupling for improved reliability.
Pulses from the accessory drive at low rpm, high load may cause a slight rattle in the supercharger gear train.
This is normal condition. No repairs should be made for this condition at this time.