Banging exhaust?

I've got a ZR TD and whenever driving over speedhumps, or on bumpy roads theres an annoying banging/knocking rattling which is coming from the rear of the car.



I fitted a de-cat pipe to my car but to get the cat off it took alot of muscle on the bolts as they were seized up real bad so I was quite violent with it.



Ever since then the noise has got considerably worse, that's why my guess is the exhaust.

All the rubber mounts are still present. is it common for these exhausts to knock? Where is the most common place?

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