2005 Chevy Optra 1.6L engine. 22200kms. Indian make.

Hi,
I have a chevorlet optra in India it has a 1.6L vgis engine and has run 22200kms and has a stick shift. Its e petrol engine and everything was working fine. Now I love my car and i've been a regular guy to get it serviced at perfect intervals with everything checked by professionals every month. Since a couple of days i've been having a problem something to do with my right rear side suspension. It is making a cracking sound of a broken spring. Whenever I drive at a very low speed(5-10 km/hr) and the noise comes only when I realease the car out of a bump. Something like a sofa spring being broken and we sitting on it. This sound is absent at higher speed on normal roads but the moment I hit a bump it comes. And the car is perfectly fine otherwise. My personal mechanic says its nothing to do with the rubber bushing and he says he will be able to diagonise the problem when the sound becomes more bolder. The authorised car service center for chevy told me that there is some "balance rod linkage problem" and that some plactic bushings need to be replaced for the lower and upper arm. And general strut o/h needs to be carried out. Well I did as per the auth. Service center and get the necessary repairs done. Well but the problem is still there though now it is a lil less. But it gives me sleepless nights that something is still wrong with it. Please help me! My friends who r in the same feild after having a test run say its rubber bushings tht have gone bad. What should I do?Both the car repair centers say my struts are ok and coil is perfectly fine. :