could be small leak in a hose or seal.this can cause the groaning noise by allowing air to enter the system.after warming/repressurizing the noise can go away.should be something simple.
Well done beerfart (?) I have it at the power steering specialists right now and he rang to say that one of the hoses has been already replaced and there is a leak in the other - apparently about $560 for the hose from Toyota, but he is having someone make up a hose for it for about $250. Still sounds expensive to me, but its better than the alternative. I'm also having new bonnet struts put in and thinking of keyless entry as I find the locks stiff and I reckon the key has to be turned the wrong way to lock and unlock them. It is not very intuitive at all.