Hi Bob, It could be the springs, but I am convinced that stick-slip also causes ND effect. To check, pushing down on the car is a bit difficult because the wings or bumper will flex too much and you cant see if the suspension is moving or the tires as as Cereal says. With the car on a lift or ramp you get under it (or lying on your back, head and shoulders under the front of the car) grab the cross-bar and jank it up and down. In my case I could not move the suspension at all with my whole weight on it but the car started bobbing on the tires with that very familiar frequency. (thats how I found out) After I sorted it I could move it up and down with very little stick slip. ND effect cured!!! Cheers J
