Was just reading about your problem. Sounds like the hydraulic damper in the rear is ruptured. It looks like the rear suspension dampers but it is on the hydraulic valve unit under the left rear. when the damper ruptures what happens is the system does it's self tests and fluid pressure drops. Then the system turns back on when pressure rises. Does the self test over and same problem.

It is pretty easy to diag. with a pressure gauge at the service valve up front.
you will see the pressure drop when you here the clicks. It also might be the pressure switch in the same valve block. The fact it does not do it while driving is a dead give away. The pump is able to pump enought to not have the pressure drop.

Give it a try.