For the last two months my wifes '98 Mustang has made this "hollow noise" intermittently when driving. The "hollow noise" is identical to the sound that is made when you blow into the top of a bottle. It only does this when starting from a stop. It also sounds like it is coming variously from the wheels. Could this be wheel bearings or tie rods. The car is an auto with 45k. Power Steering fluid is fine. No driveability problems to note. I took it in to the Ford mechanic (who fixed something else and not this problem as requested) and he said it "might" be the IAC Valve. Anyone else know what this might be. The mechanic seemed REAL iffy, especially after fixing something I didn't know that was wrong for over $1,000.00! Please, any input is appreciated.