The 3.0L engine uses four hydraulic cam adjuster cam gears that make all kinds of noise upon first start up, and if its cold does it more often while driving. In other words its normal, if you still not conviced go to any audi dealer and have them fire up another 3.0L just so you know the sound is normal, i've had to do that several times for 3.0L customers, one of the reasons audi doesn't make the 3.0L anymore.