Hi bind. Welcome to the forum. Two things associated with the sound will lead to a pull. Something in the suspension or steering system is loose or worn and changing position, or something is binding causing "memory steer".
This is a job for an experienced mechanic. The cause can't possibly be diagnosed without seeing the car. One of the first things he will want to see is if the steering linkage is the same height from the road as the lower ball joint. If it is, shifting upper components such as ball joints, (when used), upper strut mounts, or sloppy struts will cause an intermittent pull, but the clue is the steering wheel will not change position. A worn and sloppy lower ball will cause the steering wheel to change position. When the steering linkage attaches at a different height than the lower ball joint, any worn and sloppy part will cause the steering wheel to change position.
Binding parts that are not necessarily sloppy can cause memory steer. This is where the steering linkage and wheel tend to stay in the position you last placed them and they don't return to centered by themselves. The clue here is it will always pull toward the direction you last turned. If you turned left, for example, then let go of the steering wheel, the car will continue pulling left unless you physically bring the steering wheel back to centered. The car will not pull in the opposite direction as you last turned. Binding upper strut mounts often cause this problem. You will also hear the banging sound when turning the steering wheel while standing still.
To identify binding upper mounts, place your fingertips on the highest part of a front coil spring that you can reach and feel its movement while a helper turns the steering wheel. The spring should rotate freely with the wheel. When the upper mount is binding, you will feel the spring wind up then suddenly snap free and release. That is the sound you're hearing.
All of these things should be inspected by an alignment specialist. Worn ball joints can separate leading to a crash. Worn lower control arm bushings can make the car unstable and unpredictable.
Wednesday, September 22nd, 2010 AT 7:58 PM