Strange ticking noise when engine is switched off

My local dealer agreed to investigate the loud ticking noise that my 2014 Mercedes-Benz C-Class Estate makes for five minutes after the engine is switched off.

The noise seems to come from the bottom of the car at the rear. A diagnostic test did not reveal any fault and they they had no explanation for it saying it was 'just one of those things' and 'nothing to worry about'. I am not so sure. Is it a sign of trouble? Should I leave it or press the dealer for an adequate diagnosis?

Asked on 25 May 2015 by Torrepinerolo

Answered by Honest John
It will probably be either a water pump continuing to pump water through the turbo or an oil pump continuing to pump oil through the turbo bearings as it spools down and cools down. A Mercedes mechanic will be able to tell you. A Mercedes service receptionist probably won't.
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