Something in the intake is leaking air. Have the car diagnosed with an OBD II reader. It'll narrow down the suspects. It could have a loose or cracked hose or intake snorkel. Auto Zone car parts store often will OBD II check for free. Dealers will charge you about $50, for the same thing, but they have parts (should) and mechanics to fix the problems for $100/hr. You might get lucky and spot the problem yourself or the AutoZone guy'll point at what needs attention and sell you what you need.