[Motor31]

I had something similar. It was the sounds of the frame twisting due to the jack leaking and changing the set of the frame. If you have a hydraulic leak get it fixed. It doesn't take much of a leak to cause the frame to shift slightly and get the sound.

Once the jacks are down the frame is under stress, both from the weight on it and the force of the jacks holding it at a certain level. Both the front and rear jacks work against each other to help hold the rig and keep it from bouncing excessively as you walk inside.