if theyre preloaded too much it could be a cause, or worn t/c bushings.
check the pillowballs too.

also, unlike dudes said before, coilovers shouldnt really be preloaded. they should just be tight enough so that when theres no weight on the car the springs barely move.

preloading can get you lower and stuff, but it makes your car drive like a bucket of smashed dicks.