I realized when doing an oil change on my C240 today (that if the Canadian market cars are like US spec), the under-engine plastic cladding is a two-piece affair with the rear mounts at or near the mid-way point of the car.

If one of the eight (or maybe ten) bolts affixing it is missing it may make a banging noise, rain could pool on the up-side of the shield and that extra weight could make it bang.

That shield would have to had been removed temporarily for the exhaust work.