I should first mention that this is not an Audi problem, but is a concern on any front wheel drive vehicle, as well as some cars, Mercedes and BMW, which use CV joints on the rear axles.
Just in the nick of time, one of our techs noted the deep cracking on the constant velocity (CV) joint boots during a scheduled service of this car. The axleshaft is used to transmit force from the transmission to the wheel. The CV Joints allow the axle to pivot when the wheels are turned, and rotate at the speed of the front/rear wheels.
The CV Joints are covered with a protective rubber boot which keeps out dirt, and keeps the lubrication inside the joint. When the protective rubber boot splits or tears, this allows the lubrication to be thrown out of the joint, and dirt and debris to enter. A damaged CV Boot will lead to a rapid failure of the CV Joint itself, complete failure of the joint will prevent the car from moving. Often, but not always, a pronounced clicking noise can be heard from damaged joints. To minimize expense and CV joint replacement, these rubber boots should always be inspected each service for splits or tears, and replaced BEFORE failure occurs.