My 01 v6 did it and my 03 cobra does it a tiny bit. I took the seat out and checked all the bolts and put it back in and still did it... not sure what it is.
Interesting I have the same problem. It seems that the play is in the tracks.
It’s not much of a rock but I notice it.
Also not sure if anyone else has noticed that the position of the seat plays a big role in the amount of rock. Funny thing is my 04 GT had the same problem.
Mine does the same! I'm taking it in now that I know it is a warranty issue. I'll claim a safety problem as those are covered for 5 yrs!!! After all the seat is a safety device.