Whoever replaced ball joints should have checked tie rod ends, strut upper mounts and bearings, swaybar links and bushings, etc. If you are doing this yourself, as a crude test you can lift the car so the weight is off each of the front wheels. You might feel some play if you grab the tire and if so you can probably trace the source. This works better if you can put a support like a piece of wood under the lower control arm so the control arm will be moved into nearly its normal position. Beyond that you could probe gently with a pry bar to see if any joints have play or are separable.

When the car is on the ground with weight on the wheels, if an upper strut mounts is bad you will be able to wiggle the strut around quite easily by its end which protrudes under the hood. For this you can compare the suspected bad side with the other - unlikely both are bad.

Also possibly it is not a supension issue but a loose engine mount or other component?