This would have to be the biggest piece of misinformation I have come across lately The rattle is the firing which give the proplem. They not a smooth engine on firing.
An Audi A8 V8 twin turbo diesel at idle is quitter than the petrol equivalent it uses Piezo Injectors that control the flame front with up to 8 fuel pulses and is just delightful to drive I owned one for a time, great car Euro 5 compliant without using Blue Goo.