At a cold start a rattle comes from the top of the engine, and it is loudest when the car has stood for hours. The cause is the secondary timing chains slapping until the oil pressure builds up in the tensioner system.

It is not the mileage that marks out the affected cars but the engine number. The maker issued a service document for this in June 2013, and in it the examples with an engine number below 157 9xx 60 022333 are the affected ones; that runs up to production in December 2012. The engines built after that already received the revised parts.

The repair is a revised secondary chain tensioner, and with it a check valve in the oil supply passage: that holds the pressure with the engine stopped, so the tensioner gets oil sooner at start-up. The engine does not have to come out, but the work takes more than a day and costs between 3000 and 4000 pounds. On some cars the maker carried it out under warranty.

According to owners the rattle was not followed by engine damage, and there were cases where it did not get louder in six years. That does not change the fact that the revised part is the right direction, and at a purchase the question is simple: is there an invoice for it.