When strangers knock on the suspension of a moving vehicle should immediately install their source whether it is permanent or knock it appears only when driving irregularities.
A WARNING
Malfunctions in the suspension of the car can cause a serious accident!
Check the condition of the suspension is better to put the car on a platform, pit or lift, and if this is not possible, you can do the job on the free flat ground, although with fewer amenities.In any case, you need an assistant.
Diagnose serviceability of nodes transmission of noise issued by them is difficult. If you are unable to pinpoint the source of the noise, contact a qualified technician.
Faulty transmission units repair or replace (see. Sec. 6 "Transmission").