01 L rear end noise

[03DSG]

My dad has a 01 lightning with about 40,000 miles, I noticed that it has a howling sound that seemes to be coming from the rear of the truck that almost sounds like loud tires but I dont think its that. It doesnt do it at idle only when you get goind around 15 or 20 mph then gets a little louder as the speeds go up. The tires are the goodyear eagle f1 gs in the stock size and almost brand new. I have heard a car with ring and pinon noise and this doesnt sound like that....could it be wheel bearings????? low differential fluid????

 

[99_venum]

Here is a simple basic on rear bearing noise diagnostics.

First rotate the tires to see if the noise goes to the front.
No
While driving if the noise comes in and out with slight variations of throttle response then it is more than likely pinion bearings.
If the noise stays constant and only changes with the speed you are going, try swerving slightly from one side to the other. If the noise changes then pay attention as to which side makes more noise. As you swerve to the left you are loading the right bearing, as you swerve to the right you are loading the left bearing. The loaded bearing will make more noise. If the noise is constant bearing noise with no variation from throttle or swerving then chances are the differential side bearing are getting bad.

Hope this helps.