I have an 04 f150 (new body style), while driving it will make whirring sound and it will stop when truck comes to stop. I tried engaging it into 4X4 and sound goes away. Any suggestions?????
Thanks
Forgot to mention the sound is comming from the left front wheel area.

 

The answer you seek lies in a search for IWE and vacuum solenoid, grasshopper.

Seriously, do a search for IWE (Integrated wheel ends) and the vacuum solenoid that engages them. Common problem with these trucks.

 

ditto, search and you will see

 

Did what you guys recommended, did the search, ordered the parts (approx. $35.00 Canadian) and the noise went away. Thanks for the quick responses and great advice, as I am headed out for the long weekend and towing my 20 foot Seadoo boat, don't need any problems.
Thanks again guys.

 

glad to have been a help

sorry I didn't type out the fix for you, but those IWE posts are ginormous with lots of info

 

Which part (or parts) did you actually replace?