My 08 is having issues with 4x4 when i'm going down the road ill try and switch to 4H then I start to hear this very loud whining like noise coming from the front end like the drive side I then switch back to 2 wheel sound goes away I've tried many many times but keeps doing this. Now if I'm at a dead stop and switch to 4H then take off it doesn't do this. The light comes on either way I do it. Came someone help me out here thanks

 

Sounds like the IWE’s are not venting properly or a wheel end is (drivers side) my be stuck...vacuum holds the wheel ends disengaged and when you select 4H with the SOTF switch it vents this vacuum at each wheel end and allows the hubs to engage. sounds like the IWE is not moving all the way in for a full engagement.

 

Do you know what I can do to find out if this is the problem or fix it. Thanks

 

Barrow a vacuum pump from your local auto parts store and troubleshoot, unless you have the money to toss parts at it.