My 2011 4/4 sounds like it bottoms out but it is just the abnormally long seat bolts hitting the deck on certain types of road undulation, and yes in a straight line too.
I have fitted shorter bolts and painted the tip of every bolt under there with bright orange paint so I can tell what bit decks if it happens again. It has not done it since fitting the short bolts though.
Come on John admit it, you really want to fit Titanium bolts and have nice sparks under braking like the F1 boys ;-).......types someone who once fitted Titanium 'hero blobs' the small protrusions on motorbike footrests so that they sparked on corners.....only because I was too old to get my knee down or I would have bought knee sliders with flints in....ROFL.
