Can't figure out noise.

[Gary A Foster]

I have been having an issue with a noise in my 2008 4wd expedition making a humming noise while driving. The noise will usually start at about 15 mph it will continue to increase as speed increase. The noise seems to be coming from the front driver's side. After a few miles of driving the noise will begin to fade until gone. I will here the noise sometimes off and on as if 4wd trying to engage. I used a vacuum pump to test the system and found no leaks replaced right wheel bearing noise still continues.

 

[J Ski]

I have been having an issue with a noise in my 2008 4wd expedition making a humming noise while driving. The noise will usually start at about 15 mph it will continue to increase as speed increase. The noise seems to be coming from the front driver's side. After a few miles of driving the noise will begin to fade until gone. I will here the noise sometimes off and on as if 4wd trying to engage. I used a vacuum pump to test the system and found no leaks replaced right wheel bearing noise still continues.

You make sure no brake lines or anything rubbing on the inside of the tires? I had a noise once and it was a brake line that popped out of a clip that was rubbing tire and you described exactly what I had going on

 

[bobmbx]

I suspect you have a front bearing starting to complain. When you are hearing the hum, apply light pressure to the steering wheel, both left and right, and see if the hum changes. If you can alter the hum at will with the steering wheel, its most likely a bearing.

Rule of thumb: Noise disappears while turning right, its the right bearing; noise disappears while turning left, its the left bearing.

 

[Gary A Foster]

Its not a wheel bearing. I pulled the front shaft and the noise has stopped. I pulled the fluid on my front differential and had shinny metal shavings. What I can't figure out is when I did the vacuum test in the air everything was fine in 2wd but when I put the vehicle on the ground the noise would remain until I drove for about 10 miles.