I have a 2004 F150 Lariat 4x4 crew cab. Lately there has been a humming noise that seems to be speed dependent..faster then the louder/faster the hum and vice versa. It seems to be coming from down around the passenger floor and in front of the center shifter (auto shifter). Comes and goes, but when it comes on it lasts a while. I can drop the truck into 4 high and with a clunk the noise goes away as the truck shifts into 4 high. When I shift out into 2 high the noise usually comes back. I have not noticed any transmission oil on the driveway. Is this noise an indication the tranny is failing? Of note, today on my way home from work this am, I drove about 20 minutes with nothing. As I stopped at a light then accelerated, the noise kicked in..went this way off and on as I shifted in and out of 4 high to get the noise to stop. When I arrived home the noise was more of a shhhh..nothing...shhhh...nothing As one would hear from somehting out of round and rubbing as it rotated.. Something is wrong, just don't know what. I have roughly 75K on the tranny...all the maintenance was completed routinely...
Thanks,
Paul

 

This thread should help you https://www.ford-trucks.com/forums/8...then-some.html

 

Canstacker gave you some great reading material and it'll likely help you determine that you have a vaccum problem and that your hubs are trying to engage. At least that's what it sounds like based upon your description.