Great tip...found this to be the source of my 2nd row noise as well! I can't see how to tighten and remove the loose lateral sway. Were you able to tighten??? Thanks!!!Finally got around to checking out my second-row seat vibration and discovered the actual locking mechanism that folds up into he seat bottom as the seat flips forward is loose compared to the other seat. On the 60% side, both locks are virtually unlovable, while on the 40% lock there's some lateral play with the mechanism. There doesn't appear to be a way to tighten the assembly, so I'm not sure if it came this way when new or what, but it seems obvious that this is the problem.
I will find a way to fix this, even if it means replacing the entire seat. More to come...