Knocking noise from rear of Fab vRS

I remember some threads (which I conveniently can't find now) about a noise from the back of the Fabia vRS when going over bumps and sleeping policemen etc. A kind of echo to the suspension if you like, not exactly at the same time as the suspension noise.

Mine was suffering and yesterday it was in the workshop and it seems to have been cured [touches wood].

Not sure exactly what was the fault as they did three things:

a) adjust the rubber bungs that the rear seat backs rest on when upright;

re-attach a rear brake pipe which had become unclipped &

c) tighten up the mounting points of the exhaust heatshield.

I think the last is most likely to have been the culprit.