2000 A6 4.2

[Britt Crowell]

If its the newer 40v and not the 32v engine. The timing belt is still on the front and drives the exhaust cams. 
The passenger side chain connecting the cams (exhaust to intake) is in the back and the drivers side is in the front. 
They use a hydraulically actuated chain tensioner to advance the intake cam. The plastic shoes that the chain rides on, can fail and the chain can jump the sprockets and bend valves, just happened to my father in-laws '01 A8L. There are also locking pins in the tensioner that can fail on the upper hydraulic part and the bottom is spring actuated.
At start up it appears to be common to get the rattle as the engine ages.
There is a good post on QuattroWorld with pics under the valve covers of doing the passenger side, the drivers side requires removal of the timing belt as the rear timing belt cover prevents removal of the chain tensioner.
Look for "Replacing cam chain tensioner and/or pads on bank #1 of 40V motor" on QuattroWorld in the D2 A8 list under the FAQ Digest at the top. Lots of pics
http://forums.quattroworld.com/a8/msgs/55496.phtml <http://forums.quattroworld.com/a8/msgs/55496.phtml> 
I'm planning on doing my wife's '01 A8L with the timing belt in the next month. Getting the pads on Amazon. It appears that all the engines of this type I4, V6, V8s use the same pads even though not all the suppliers list all the engines models.
 
Britt
------------------
Checked out a 2000 A6 4.2 that a friend of a neighbor had on test drive from
a used car dealer.  Right after startup as the engine settles back to idle,
there's a momentary rattle sound from the engine that sounds sorta like a
timing chain rattle.

When did the more modern V8's move the timing drivetrain to the back of the
engine?

Ed