Hope someone can help.
I just purchased a 2007 f150 5.4 4 x4 with 88k.
When driving occasionally a grind sound will begin, turn the 4 x 4 switch to high it stops.
Then I can resume in 2wheel mode for a few miles that it will begin to grind again.
Any ideas??

 

You should read up on the 4wd system on your truck, there is a ton of info in this forum that describes exactly what you are experiencing.

Start here.. This will probably answer your question
https://www.f150online.com/forums/ar...then-some.html

Could be a few things but i believe the first thing to check should be the solenoid.

 

Thank you for the post.
It was extremely helpful. Heared this forum was awesome this confirms

 

Glad to help, just always hit the search function first. You will find the answers to almost any questions you have, already discussed on the forum.

Goodluck!

 

What you have is a IWE that is likely leaking vacuum. IWE's are the vacuum actuated hubs that are used to lock the wheels to the front axles. Very common problem.