Helllp - 2015 A7 New timing tensioner

Hello, 

Newbie here after some urgent help? Afyer sending my car in to Audi to have it checked due to a 'tapping' noise that tends to be on cold start up and last around 30 - 60 seconds, only a couple of times a week, Audi are telling me it needs a new cam belt tensioner. The car has recently had new cam shafts (!) due to a previous fault done by the previous owner under a good will scheme. I am now being told another ~ £3800 repair is required... 

Is this is know fault and would it not be fair for me to assume that if the cams have been replaced, then so should the belt(s). and if so, when you change the belts is good practice to always replace the tensioner too... The car has only done 25k miles now and the cams are probably still under warranty meaning surely so should the tensioning side of things. Not to mention, its got full ASH and only done 25k miles. 

At the moment I am being offered a good discount and no cost for parts but I still stand to pay over £800... 

Any help or past experiences are much appreciated. Love the cat but this will be its SECOND major engine strip down...