Hi. When I drive my '88 420 SEL over a bump there is a knocking noise coming from the front right suspension. The bushings/joints were checked and there is no looseness/freeplay. The car just returned from the shop and the right idler arm was one of the repair list items completed. The use of a chassis ear system has been recommended to pinpoint the problem. Does anyone have any experience with this type of diagnostic tool? Does anyone have any idea about what might be causing the problem? Thanks.