First, this being my first AWD vehicle (2003 X Type, 2.5, auto trans, 120,000), it may be a normal noise. But instinct tells me it is not.

Here is my attempt to describe the noise: It has a slight metallic sound, but not squealing, whining, nor chattering. It is not overpowering - more of a quiet drone, or a low-pitched rub somewhere that may need lubrication. The sound seems to come from somewhere below the rear half of the car and increases in volume and develops a slightly higher pitch commensurate with increased speed.

If the AC fan is on med. to high, or the sound system is set at a moderate level, you will not notice it. But the noise has become more noticeable over the last 150 miles, or so it seems to me. It completely goes away simultaneously/exactly with the car coming to a dead stop.

Any suggestions? Wheel bearing? Transfer case?

It should be obvious to all at this point that I'm no mechanic!

Thank you in advance!

 

Time, what you are describing sounds a lot like the carrier bearing for the rear driveshaft. Fortunately, this is an easy fix to atleast make the noise less. But, this will also just put off what will ultimately need to be done.

For the moment, you can lift up one side of the car (so you can crawl under it) and using a grease gun (loaded with termiline grease) and a needle attachment, you will want to slide the needle attachment into the carrier bearing in a few different spots and add some grease there. I bet you will find that your noise will go away. But, what this is also saying is that the bearing is starting to get worn out and at some point in the future you will end up needing to replace the carrier bearing. The good thing is that by simply greasing it, you can most likely go another 30K+ miles before needing replacement (more noise will clue you in that it is time). A simple shake test of the driveshaft will tell you when the bearing is toast (if it moves, it is done).

This is a common noise with our cars and most have been able to fix it by simply greasing the bearing.

 

Thanks for your insight! Will try it!

 

I just had the same sound in mine when the car was cold. It lasted for another 600 miles then while driving at 40mph my transfer case exploded leaving parts on the road. I suggest you have a shop do a quick check on yours ASAP. You can find a used one with low miles for way less than the 4k the shop will want.