I'm not sure about the Gen III, but in the Gen II it's under the passenger seat. Take the car back to the dealer. It's still under warranty.
Yes I think the audio amp is under the passenger seat on the Gen 3 also. The unit under the driver's seat is the satellite receiver, if you have one.
My entire audio system died on my 2011 with 10k-either no sound or intermittent sound with buzz from all features-(radio, mps, cd, etc). Dealer tried amp replacement-but it did not solve problem then ordered entire new system to install. I have to wait 2-3 weeks for part.