I ve just bought a Audi A4 3.0tdi Quattro 218ps(2016) with 78k what's people opinion on change the chain as from what I researched theese  chIn can stretch...and the chain guides can wear some advice would be appreciated 

Edited August 19, 20223 yr by Philrc

Normally the chain will start to clatter I believe. If it sounds smooth then I would leave it in my opinion. 

It's an engine out job to change, with the costs that  come with that.  When I had mine done it was a guide which had broken,  horrible clattering noise when the engine was under load but only for the first minute or so when starting the car from cold, also couldn't bear it with the windows up.  My chain had stretched as well but I believe it throws up a timing error if it stretches beyond a certain amount which mine hadnt. 

Change the oil every 10k not 18 supposedly helps the lifespan of them.  There is no recommended mileage to change the chain/guides,  it's not the same as a timing belt in that respect.