Intermittent Vibration Sound, possibly from exhaust

[RAS]

I had a great 300 mile round trip to the Welsh Borders. Unfortunately on one of the narrow lanes I ploughed through a drift of gravel and since then I have an occasional vibration noise that sounds like an exhaust baffle is loose.

I've checked underneath this morning and I think it may be coming from something that looks like a 6" diameter and approximately 8" long cylinder that is covered with some form of mesh which is inserted in the exhaust pipe between the sump and the exhaust under-tray. Its is the lowest point on the car and it rattles a little when knocked.

I've checked the bible and I can't see any reference to it, is it standard and what is its purpose?At present I intend to ignore and see if it gets any worse.

Any advice or guidance would be appreciated.

Many thanks
Roger