I'm noticing a whistling sound coming from the rear on my Expedition. Not very loud and originating outside the truck. It is intermittent and occurs when the truck is idling at a stop and when it is in motion. Anyone experience this type of irritating sound?

Thanks,

 

do you have rear air and/or the air suspension? If so I would start there.

If not it could be your fuel pump. Do you regularly run the tank down to below 1/4?

 

Thanks hcmq,

I don't have air suspension.
I do run my gas down to 1/4 tank, but I drive a lot and fill up twice a week. Is the noise a sign of fuel pump trouble?

 

No prolly not. Some are just louder than others. If you are really worried about it have a competent mechanic pressure test the system.