My girlfriend has a 208 1.2 and hit a bad pothole today. Now it has a weird rattle/vibration under medium/hard acceleration. It steers fine, no knocks or clonks over bumps.
Could be the cat internals breaking up. Tap it with something and see if it rattles. Might be worth checking the rest of the exhaust for cracks etc too.
Loose heat/undershield? It may be that a heat shield that was already rusting at a fixing point has broken through and is now rattling. Time for a crawl underneath!
Either of the above is quite possible, my money would be on a heat shield, nice easy fix if it is, just remove screw/nut affected & put a big washer behind it, job done.
