High Pitch Whine?

[Rangerman1987]

I just recently purchased a used one owner 2003 Explorer 4x4 with 120,000.
Overall it is in really good condition and looks as though it has been well taken care of and maintained. The only issue that I have noticed so far is a high pitch whine only when DECELERATING at low speed? I have checked other posts regarding this same issue on this forum and have narrowed the problem down to two possible causes.
Differential issues or rear wheel bearings.
I am leaning more toward the differential being the culprit although I would like to get others opinions who are more knowledgeable than I am.
Where do I start, check wheel bearings? Replace fluid in the differential? With what?
How long do I have at 120,000 before this turns into a major problem?
Can I just keep driving it this way and hope for the best.
Is this problem common with just 2003 Explorers, or all of them in general?
Any help/advice/opinions or simular experiences and courses of action would be greatly appreciated.
Thanks.

 

[Number4]

Have someone else drive while you sit in the back. See if you can pinpoint the noise a little better. Hearing noises from the drivers seat can be real hard to tell where it's actually coming from.

 

[Rangerman1987]

Have someone else drive while you sit in the back. See if you can pinpoint the noise a little better. Hearing noises from the drivers seat can be real hard to tell where it's actually coming from.

Yes, I have. It is more pronounced now. Again from what I've read so far it sounds like it is coming from the rear differential.
It is dissapointing but anything mechanical is prone to wear out, I understand that. I just thought maybe changing the fluid might buy me a little more time before I have to have it rebuilt/repaired.
Or just drive it until it becomes more of a problem as long as that does not cause more damage or affect anthing else?
With 120,000 on it now I am curious as to how long it had this problem before I bought it?
Thanks for your input Number4, I appreciate it.