Knocking sound coming under the car, don't know where coming from, if the weather is warm or hot i hardly hear the sound, but in cold weather, the sound becomes louder.The knocking sounds only if the car is in motion, but on neutral idle no knocking sound . I have a mechanic check and he diagnose it need a new motor mount. is that true.
a knocking sound underneath my car in cold weather. Tachometer is steady . on 1999 Mercedes-Benz SL500
very poss or drive shaft joint