Audio Systems: Pulsating noise on low band a.m., freeway overpasses, window antenna

Question
I have a 2004 Ford Expedition with an antenna built into the rear side window.  I get an intermittent pulsating noise on a.m. 980 (and low band weak receiption stations).  It gets worse when I am in a poor reception area and expecially under the freeway overpasses and can best be described as sounding like the whop whop whop of the blades of a helicopter!  If I come to a stop the noise will stop, but if I slam a door or the tail gate, the noise will come back, even when the engine is off, and then it will last for about a minute and will cut out.  All of the after-factory items have been taken off line and my dealership has replaced the radio, the wiring harness, isolated the antenna cable and even tried a differnt style radio and also replaced the rear side window with the built in antenna.  The noise persists... and here is the even stranger part: when the "message center" lights up "low feul" the noise goes away until I fill the tank again.  
Today, they are going to "paste" on an external antenna to see if that makes a difference and if it eliminates the noise they plan to drill a hole in my fender and bypass the window antenna ... but I would rather have the problem fixed than simply "bypassed."  Any ideas?
Bob Rentzer (818) 521-5000  That is my cell phone which can't be called collect but if you call my office collect (818) 758-1919 and give my secretary "Dora" a number I can reach you at before they drill into my fender, I will give you a call... otherwise I will delay having the hole drilled and wait to see what you write back on email.
Thanks in advance.
Bob Rentzer

Answer
Bob,

it sounds like you have some more serious problems than just the radio , if other electronics directly affect the reception and noises , i think your dealer that is doing the repairs needs to give your main harness that supplies the entire car with its electronics a good go over with some diagnostics to check for broken/loose/frayed/cracked/or damaged wires and also for any shorts within the system, because most cases with average distortion in the AM reception can be traced to the radio / radio harness / antenna or antenna cable and some just need a booster to get better reception , but what you describe could be a serious wiring problem, so i would recommend to the dealership before they do any bypassing to take a look at your main harness that controls you dash lights, fuel sensor, ect.. and make sure they understand all of the ODD occurences that cause the noises, so they can have an idea of where to look at .. hope this helps you out sorry i cant get you fixed up but if you need anything else let me know

thanks