2004 FX4 has a whine in each gear under acceleration and deceleration. Whine pitch and loudness ramps up with vehicle speed. The problem was initially thought to be rear diff gears but the noise is actually coming from the transfer case. The noise completely goes away when the torque converter is in lockup. It doesn't sound like a typical torque converter bearing failure as it is quite faint. Stalling up the converter doesn't make the noise either, only when the truck is moving. Any ideas?

 

Sounds exactly like the problem I have now. I just posted in the 2004-2008 category with no responses yet. I will probably be bringing it to ford next week seeing as I have a steering issue as well (just turned 20,000 miles ) and earlier my abs light came on then went out. I hope this is not a sign of things to come. I will post here when I find out what it is.