e420 rear suspension creeking
 

i keep experiencing mederalty loud creaking sounds coming form both sides of the rear suspension when the suspension travels. i havent been able to isolate the sound. i can reproduce the sound at standstill by pushing the car up and down. my mechanic recommended spraying the bushings with lithium grase claiming that this stoped the squeaks on most of the bmw's, however it didn't help much. the suspension looks to be in good shape and i recently installed bilstein shocks all around.
any suggestions!