I have similar "clunk" issues too. My Chevy dealer gave me the attached document to keep and read. It's not specific to Camaros but explains what they feel is "normal".
The tech checked suspension and driveline components on the lift, checked for GM documentation, test drove my car, and tested a new one off the showroom floor. Both vehicles had the noise under the same conditions.
Based on what I'm reading, my symptoms point to gear rattle and/or backlash.
2012 2SS/RS 6sp Man SW - She's a mod tea-totaller but itching to taste her first sip of "white lightnin"