if its only started since the ball joints were done, then go looking there first
possibilities (apart from ball joint related) ..
strut to hub bolts losoe
strut top bearing stuffed or 3 nuts loose
damper coming loose inside strut housing or at strut top centre nut
rack end or tie rod end, worn out
rack loose on mounts
tie bar bushes worn out or retaining nuts/bolts loose
sway bar links worn out
sway bar mounting cracked (usually you hear a clicking noise)