front differential on 2002 Ford F-150

I have a rumbling in my front differential on my 2002 F-150 4x4. What am I looking at in cost to repair.

Asked by for the 2002 Ford F-150
Or, you could have transfer case noise...being that it's in the same general area and is part of your drivetrain.
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A diagnosis has to be performed to determine what the noise is coming from. It could be a bearing concern or as simple as a vacuum line leaking causing the 4x4 to be partially engaged.