From what I understand it's some sort of internal bump stop that makes the noise. It's only under light compression. For example, when I come home and go over a speed bump they will make a sort of thump noise. It won't always do this, it depends on how fast and the angle I hit it. Any other type of driving this is nonexistent. So whenever off road I will get the noise but It's nothing that worries me due to the great performance they had this weekend. I think it needs to be addressed in future RADFLO designs. Other than that it's the best ride I've had on a 4runner setup and the smoothest.