noises

Check for a bad sway bar link. You'll see a short rod at the end of the sway bar, try pushing and pulling the rod and see if you feel any movement in the ball joint ends. Here is a pic of the part: http://bit.ly/7y8dO8 Look at item #23

in 98 the a6 sedan was a "c5" body style, the wagon was a "c4". which is yours? if its a wagon, check the upper control arm outer ball joint end by placing one hand at the top of the wheel and one at bottom with the wheel off the ground. twist back and forth to check for play. although bad rear shocks are rare, this could make noise on any car and should be kept in mind (look for leaks too).