I recently purchased a 2000 A6 2.7 biturbo I now notice a noise coming from the engine bay when the car is idling and warmed up( not present at first whencar is cold)it almost sounds like a diesel rattle when I rev it up it goes away as soon as the car idles down it comes back..any ideas? Ihave a 30 day warranty (power train)that runs out in three days so if this is critical ie; timing belt, water pump, or turbo i need to know so I can pursue getting it taken care of by used car dealer, what I don't need is a huge repair bill since I just shelled out 2,500.00 on down payment and a car loan to boot since I am disabled with MS. and on a fixed income I am desparate for some advice
to clarify noise a little better ....it has that dull sound of shaking marbles in your hands.... in other words I noticed NO noise nice and quiet as it idled and a few days ago this dull rattle(louder with hood open) started (only when idling) which when revved up a little it

NOW stopped at a light the car seems to run a little rough @ idle..............................Please if any one has an idea.is it a pully or is it a timing chain or the turbo

 

when you said marbles the first thing that comes to my mind is a bad waterpump. Would have to hear the noise. I can tell u it's not the turbos, they make an outragious drilling sound under boost(you will know believe me you wont be able to drive it). The belt wont make noise it will just go.

 

thanks for the response i too thought it might be the water pump.......when i say marbles I mean somewhat muffled but enough clacking to think it is either that or a tensioner pully. when I look down the front the pully on the very top looks as if it is not spinning true9 what is that pully for? But more distinctly it sounds like a tensioner spring or arm binding I think....it does though sound as if it is coming from external engine rather internal engine

 

could be a bad tensioner take it to a shop or get a long screw driver and hold it to the tensioner and hold it to your ear. You can use it as a stethoscope