ye..all vibratehnics are under car.......well to end the story..i couldn't believe it..stopped at petrol station and added some air in rear tires....result.. no more sound from the back off throttle....i pumped them till 2.2 bar..than i released them till 2.0 bar for check only.. again same story so filled them again to 2.2 bar...all quiet..go figure..anyhow thanks for replies...