Engine rocks wen I release accelarator

Please help had same problem in my escort driving along in 2, 3 gear just gently plodding along but wen I release gas pedal car seems 2 rock just 1 time but it is so annoying u only av 2 rest ur foot on pedal n then release it for the car 2 do it every time n it cant be helping driveshafts or mountings at all please im desparate. It is only a slite rockin motion but enuff 2 not enjoy driving my car. Car is like new in every other way