Humming/Howling/Resonance When Cold Started

[killitngrillit]

Maybe its just the WI changing seasons or something is going bad. When I start from cold I can hear this sound outside my X. I noticed it wasn't there when its warm. I suspected the fuel pump or the air box but I'm not sure now. I can't hear it inside. But if I walk around the outside it's fairly noticeable; I would call it a mid range pitch of sound.

Anyone ever have something like this before?

2006 4.0

 

[Davidm53]

The cooling fan could be affected by the cold, and pulling more until the engine warms up.