Humming noise

[John Christopher]

I have an 03 expedition and I get a humming noise between 40 and 50 mph when on the gas. If I leave
off the gas or change the speed it stops. It seems to be coming from the engine compartment. No one has been able to tell me what is causing it. Any ideas would be appreciated.

 

[Hamfisted]

Not missing a pet cat or anything are you ?

 

[John Christopher]

No, I can't say I am. By the way that's a great picture.