I came across this info from www.techauthority.com
2011 Dodge Challenger Owner's Manual 1st Edition PDF ( English )
Due to the high performance nature of your drivetrain, you may hear your transmission. This can be most noticeable when the vehicle is idling in NEUTRAL with the clutch engaged ( clutch pedal released ), but it may also be heard when driving at low engine RPM. Also, this may may be more noticeable when the transmission is warm. This is a normal condition and is not an indication of a problem with your clutch or transmission.
This pretty much sums up what I'm hearing.