Could be the power steering (check the fluid level) and bleed for the air to escape. Bleed by turning steering from lock to lock a few times. Then try bleed procedure again after a few hours.
or it could be the Moose problem if it sounds similar to this...
http://www.sanpedro.com/sounds/foghrn10.wav
To fix Moose problem, put hose clamp in the middle of 45 degree hose (between the IAC valve area and inlet duct (accordian tube). Tighten until the moose (foghorn) sound is gone.
