I have a 2007 F150 with 21K miles, 5.4 with electronic shift-on-the-fly transfer case. 4 wheel drive works fine. After switching back to 2WD and driving about 4-5 miles a grinding noise starts. Low level at first then gets stronger. Only on acceleration. You can coast down hill at 50mph, no noise. Step on the gas it's back. Now the good part. Switch to 4WD, and the noise goes away. Switch back to 2WD, and it's still gone, for about 4-5 miles.Thought it might be the hubs, but why no grinding noise while coasting. Only while depressing the gas peddle? If you shift to neutral and race the engine, no noise. Only in "drive" under load. Give it gas going down hill, no noise. Any thoughts?

 

Not positive but sounds similar to what happen to my '07, however, I was in 2wd the entire time when the grinding noise happened. It was the IWE solenoid. Your truck should still be under warranty, its a quick fix at the dealer, they should be familiar with it.

 

Thanks ZEEKA. Yes the noise is only in 2wd. Switching to 4wd and the noise is gone. But, did you get it only on acceleration?

 

I got it just driving down the street at around 35mph. I'm not exactly sure how it works but basically the IWE solenoid keeps the front hubs from engaging into 4wd when your in 2wd by creating a vacuum in the lines that run from the solenoid to the wheel ends. I'm not a mechanic so don't quote me on that but thats kind of how somebody explained it to me. The solenoid is on the passenger side of the firewall in the engine compartment. It probably got some moisture in it and caused it to malfunction. They'll replace it with a different designed solenoid so it doesn't happen again.