Mine does it too! I can get it to do it almost whenever, if I wanted to. The floor pan just past the pedals seems thin and maybe it was not curved properly or something when assembled. I can get nearly the same thing to happen if I push down some on the top of my crapalier.
It's annoying in the stang - considering having the dealer fix it with my next "free" oil change.
'97 Cobra Vert - sold
'06 GT Sold 6/2010
Current: '06 F-250 Diesel, '10 CR-V, '11 Civic (Lease)
Ordered 12/12/12 Built 1/25/13 dealer received 1/30/13
2014 GHIG V6 Stick w/Perf. Pkg