2005 Scion xA sucking noise from intake

I have a 2005 Scion xA, automatic transmission, 48,000 miles, and in the past 4 days it has been making a sucking sound (like a straw sucking in air) from the intake area on the front of the engine. I have taken it to my dealership and they can find nothing wrong with it (they checked the hoses and everything around there including the internal air system). Any help is very much appreciated. And it gets louder when more throttle is applied, but definitely sounds like air.