[jblackburn]

Probably the right rear shock absorber.

See if your rear shock looks like the one in this thread (at the top):
http://www.cruzetalk.com/forum/12-g...5881-extremely-loud-rear-shock-absorbers.html

 

[jblackburn]

I'm wondering if it's related to this TSB even though my car is a year newer: Rattle or Clunk Noise from Rear of Vehicle When Traveling Over Bumps – 2011-2015 Chevrolet Cruze | gm.oemdtc.com

Quite possibly. Same issue as the thread I linked above.

Mine rattled a bit though despite my rear shocks looking ok.