I've just found the source of an annoying "knock" that happed randomly, never constant, smooth or rough roads may or may not generate the noise.
As Lambert said it was the exhaust, in my case the rear silencer box was hitting the towbar cross bar.
Shaking the exhaust via the tail pipe DID NOT result in the noise, however a shake via the mid pipe and the knock was present. It was the second rubber support on the silencer stretching with age ( furthest away from tail pipe), in essence lowering it close to the crossbar resulting in a very random knock.
Worth a check but you need to get under the car to shake the exhaust.
Good luckMike
Yokohama Geolanders, Sony head unit, NAUTILUS Air Horn, DRL conversion, Rear cargo space, Elvis Bobblehead, transfer Guard, Indian hanging Elephant, Koni Heavy track dampers, Custom SS exhaust, Voodoo Doll, Adventure Rack with LED ight bar, vintage ERIBA caravan usually attached (yes it's slow)
