The change in pitch depends on a few different variables. If the increased volume of air being sucked in causes the orifice to deform it could either raise or lower the pitch depending on how it deformed. What I would expect from increased vacuum is an increase in loudness, not necessarily a change in pitch.

I would suggest taking a piece of 5/8" hose and listening around the base of the steering column with the engine running. That will help you pinpoint the source of the leak.