In this video I have a great example of what squeaking ball joints sound like. Squeaking ball joints can squeak when turning or going over bumps. A squeaking ball joint is usually caused by poor lubrication which is the case with the vehicle in the video. The ball joint boots busted quite some time ago allowing the lubricant to escape and allowed water and dirt to get in. This caused rust and a rough surface to build up on the ball and in the socket causing the squeaking noise when the joint is articulated.
Note: This is just one way in which a ball joint can fail. Many times ball joints can clunk, knock and rattle due to excess clearance built up in side the ball socket between the ball and the socket.
Disclaimer
This is just one way in which a ball joint can fail and is only and example of the noise a ball joint can make if it has failed in this way. As mentioned in the video a ball joint can also make many other noises. This is only an example of one noise it could make. Also, a proper stethoscope or chassis ears diagnosis should be done to pin point the exact location of the noise you are hearing. Other components in the steering and suspension system can make similar sounds. This video is not intended to show how to properly diagnose a faulty ball joint. It is only intended to show you an example of one noise it may make.