How to check if a collision impact is perpendicular with the velocity of the collider?

Hi, I actually wanted to play a "thud" sound when the player (a car using SphereCollider as the wheels in my case) is hitting anything, especially the ground. Currently, the sound always plays because the SphereColliders would always trigger the OnCollisionEnter method even when they roll (not only when they land on to the ground like what I would like to do). So I was thinking that maybe I should check on the impact of collision (either the angle and / or the magnitude of the impact) to determine whether or not I should play the "thud" sound. So, how can I check the impact collision?

Thanks in advance.