power steering noise on 2001 Cadillac DeVille

When my car is running there is a hissing noise. The noise goes away if I move the steering wheel just a tiny bit in either direction and hold it. If I let go, the noise persists. The power steering pump was replaced 2 months ago. Good this be some sort of a vacuum leak as I believe the pump is not belt driven.

Asked by for the 2001 Cadillac DeVille
add pwr steering fluid
Fluid is full. cadillac service man said that when the new steering line was replaced it may be up against the frame rail and when the pressure (hydraulic pump) chnages it moves away from the frame. ever heard of this?