I'd say lower control arms. I'm having the same problem and thats what it seems to be on my end.

99 Blk SE Sport 2.5 CD4E Euro Focus SVT Wheels 5 % tint Mesh Grilles w/indiglo ford KKM intake filter FMS 9mm wires Superchip Signal mirrors Fog lamp mod Dingless A6 sidemarkers Duals SVT springs/struts