I had exactly the same issue; a clunking I couldn't locate. Was told it was the rear shocks, but it wasn't.
There's a real good chance it's your rear sway-bar bushings, this is a well-known issue. I ordered poly-urethane bushings for the sway-bar and the drop links, and it completely cured my clunking.
2012 GT Premium, Brembo PP, MT82, 3.73s, Blk/Blk. Bama 93R, Koni Yellow Rear Shocks, Hawk Ceramic pads, Luxurious & Plush Floor Mats
Last edited by NoVa5.0; 03-10-2016 at 02:23 PM.