Control arms make up the linkage suspension system on your Audi (4 arms per corner).

2 types of Control arm wear...

BUSHINGS
The bushings in the control arms are made of Urethane. This is softer than polyurethane, and therefore is quieter and smoother than your average control arm manufactured. But it dries out quicker, and because of this the bushing starts to squeak and needs to be replaced sooner. If you turn your steering wheel, or go over a bump and hear a noise like 2 balloons rubbing together, this is likely your problem.

BALL JOINTS
If a linkage does not connect via bushing, it will connnect with a ball joint system. Over time the cup of the joint will stretch and enlarge, allowing the ball to slop around. When you drive over a bump and hear a clunk, this is the slop that you hear.

The ball joint problem is more a safety issue than the bushing problem. If the ball cup splits, the joint can come apart - that is not good. The bushing squeak simply will get louder and is annoying, but the urethane of the bushing itself will last quite a while like this.

Replacement or Fix
You cannot replace just the bushing (in most cases). Audi determined that the labor costs of removing the bushing from the arm and replacing it is higher than the material cost to simply replace the full arm - so they do not sell the bushing separate. An arm with a bad ball joint cannot be repaired and you must replace the entire arm.

Sometimes a bushing can be quieted by injecting grease inside the rubber seal grommet that covers the bushing (upper arms). The lower arms have no grommets - so sometimes a good spray of WD40 will quiet them.

EDIT: There are now some replacement bushings available. You will require a press to get the old bushing out and the new bushing into the control arm. But at least now we have options for many of the control arms.