[BB]

I don't know this works for others, but just for your information.

Today I tired one little thing, and there is no groan sound now. What I have done is to lower the right front a little by torsion bar adjustment (equalize the height of left and right front), that's it.

I guess that ABS was activated and it made a groan sound from the right front, becuase the height of the right front was higher than the left and the weight of the vehicle intensively moved on the right front tire when braking on a downhill road.