I bought the car about a year ago and it’s had a suspension knock since I bought it. I have replaced shocks, struts, springs, inner and outer tie rods, and sway bar end links. Could it be caused by ball joints? It drives well and doesn’t have any symptoms of bad ball joints. Could it be the power steering rack going bad? I’ve noticed a small leak in the rack but it’s so small i don’t notice a difference in the fluid levels even after months of not tipping it off.

 

You could have worn strut mounts but they should have been replaced at the same time as the struts.
​​​Another possibility is worn control arm bushings or worn sway bar bushings.

 

Did you change suspension parts with Poly bushings? Did you replace upper strut mounts? Is the knock in the rear or just in the front? Did you check ball joints? (raise car get a 3 foot bar under the bottom of tire and see if you get movement). I don't think the rack would give you a knock unless it is loose, bad bushing on sway bar would give you a knock. I would be more in favor of ball joint or strut mount if not change when new struts got installed.