That's true. About once a week a C-5A flies in and out of the Corpus Christi Naval Air Station. It has very loud engines. The engines on Air Force One are much quieter. Compared to lots of military jets like F/A-18s (ever been directly under the flight path of an F/A-18 during take off or landing?) a 747 is actually fairly quiet. Considering most of the planes flying in and out of Baghdad International are military and are flying approaches to the airport meant to minimize the ability of terrorist on the ground shooting them down with SAMS rather than to minimize noise, I doubt Air Force One made as much noise as most of the jets landing at Baghdad. When you consider Air Force One landed at night with it's lights turned off and just a crescent moon, I doubt people on the ground were able to see it very well as it made its approach.
No kidding. C-5's sound like a cross between a coffee mill running wide-open and a bank of air-raid sirens stuck in first gear. Loud as hell, you can recognize them anywhere. I seem to recall seeing an early-production or prototype C-5 or C-5A groaning around over Charleston or Jacksonville back in 1970, or maybe Patrick AFB, and noticing its peculiar sound.