Do not know if you solved your issues, but if you do not know
A common issue with the C5 and C6s is the bolt for the pulley off crank uses a torque to yield bolt
Once it has been installed it stretches and cannot be tightened and has to be replaced
Some not wanting to do the correct repair use a red locker on the threads but later on if needing to take the bolt out it will be quite impossible to get loose
Proper way is the steering rake has to come unbolted and have to swing it to the drivers side to get it out of the way to get to the bolt with a wrench
Make sure getting a new TTY bolt
To proper torque the bolt the crank has to be locked down, so it does not turn
Most take the starter out and clamp down the flywheel or flex plate with a tool that is made for that purpose
Make sure pulley is not bent and the belt is turning straight and true.
Do not bang on the pulley or bolt as the CPS can get damaged, and now you have a much bigger repair
Some use the old bolt to seat up the new pulley and then replace it with a new TTY bolt.
Not fixing this correctly can cause the crank position sensor to trip false misfires and engine yanking out timing causing performance loss
As to rear noise, check the muffler mounts being loose, also check the end links of rear sway bar and assure the rear end fluid is good and filled properly
Else could be the driveshaft bearing inside the torque tube
