I have a 2004 F150 4x4 Supercrew Lariat. For the past couple months when I accelerate at highway cruising speeds there would be a strange sound coming from what sounded like the engine. I apologize for providing very little details on the sound but it is very hard to put into words. The last couple weeks it has started to happen every time I accelerate no matter the cruising speed. I read a few threads about similar problems and it seems most say it is the alternator bearing. I took my truck to the shop yesterday and they couldn't pinpoint the problem. They said everything appeared to in good condition. They eluded to a tranmission problem. This is outside of their realm and referred me to a transmission shop. This morning in my attempts to narrow down the problem I put it into 4 high. The sounds completely went away. Any idea what could be wrong? It only happens in 2 wheel drive. Thanks!

 

either the 4 wheel drive solenoid or a bad IWE. do a search. lots of info here about it...

 

With no description of the sound whatsoever, it's kind of difficult to help you. If the 4x4 engagement makes the noise go away, you can try this...

http://www.ford-trucks.com/forums/83...then-some.html