Whirring Noise While Driving

[short1]

Hey, I've been getting a whirring noise for the last week on my 06' v6 explorer with 107k. It almost feels like a broken belt on a tire or a bad wheel bearing. Tires are less than a year old and wheel bearings about the same. Brakes are all good. The strength of whirring vibration felt on the floor and through the steering wheel varies. The sound/feeling doesn't change in relation to engine speed or if I turn the wheel either way, so I'm pretty sure it's not wheel bearings. It goes with vehicle speed, no change whether i'm accelerating or coasting/stopping. It's not always there either. Sometimes it does it right away but goes away after a mile or so, sometimes it doesn't start until a bit down the road. Today for instance I went to pick up my son from school, no noise the way there, but when we left it was whirring. Got up to about 50 and is sounded/felt like i had big knobby tires or was going over a grated bridge. It has never been that loud. Had to stop at a red light, when it turned green and I took off it was a quiet and smooth:scratch:. I have no idea where to start or what it could be. I did a visual and don't see anything hung up or dragging underneath. Any suggestions are greatly appreciated. Sorry for the long post, trying to be as descriptive as possible.

 

[Flag Gibby]

Check your brakes/calipers/rotors; you could have a problem with the rotors that could present itself that way. Any play in the front differential?
One way to check if it is in the front differential is to lock the vehicle in 4WD and drive around with it that way and see if the vibration is always there; at least then you would know that it is isolated to the CV joints,U joints and differential in the front.
You can follow these directions to test the CV joints without driving the vehicle around in 4WD Hi: http://wiki.answers.com/Q/How_do_you_tell_if_Ford_Explorer_CV_joints_are_bad

 

[short1]

Thanks for the reply! I doubt it's the brakes since there is no change when braking, will inspect them though. Is it safe to drive it in 4x4 on dry ground for a short period? I thought I read somewhere it is bad for the drivetrain. Should I run it in 4hi or 4low? Or does it not matter? I don't think I've ever used the 4wd since I've owned the truck

 

[Flag Gibby]

If you are going to test, do it only in 4-hi and don't get crazy with it just run it around for a trip or two at speeds less than 60 to test it out to see if it is always making the noise or not. Highest probability is that it is in the transfer case or is a CV joint, but really hard to say based on the symptoms right now.

 

[short1]

Well I ran it up and down the road a few times in 4high, brought it up to about 40, never made the noise. I'm stumped as to why this would be an intermittent problem.

 

[Flag Gibby]

The only thing I can come up with is that it is a bearing with a bad wear spot in it so it is not always rolling on the bad spot.

 

[short1]

Thanks for all your help, I guess i'll just take the wait and see approach!