first, i am not an expert on this subject. i may be wrong. I think the sound you hear will tell more about about which part of suspension system goes bad. say if you hear sound with more treb, it may be produced by the metal ball joints like the ones in steering system. if the sound has more bass, it may be the rubber bushings
if I were you, i would bring the car to a shop, getting them to thoroughly check your suspension system. some of the parts e.g. ball joints are not able to be checked for worn out without removing the connecting parts. for example, the front upper control arm ball point need to be removed from steering nuckle and flipped back and forth several times with a torque gauge (good specs for ls400 falls within 10-35 kg-cm according to lexus repair manual)
removing things, checked and then replaced if needed, reinstalled if no need wont damage your car if done by a good engineer
hope this helps