Whining transmission

I have noticed a slight whining noise in the automatic transmission of my 96 Blazer. This is a high mileage auto (170,000). It isn't low on fluid, but could use a filter change. I have not noticed any change in performance, only the whining noise. Any help would be appreciated.

When does the noise occur (under what operating conditions)?

If the whine is only present at idle RPM after the engine and transmission are fully warmed, it may not be a problem. If the noise occurs while moving, but only in a particular gear range, that may or may not be a problem.

is this a 4 wheel drive?? if so it might be at the rear?? i bought a 4 whell drive ford f-150 and thought it was tranny..i was right 2years later.
i've also heard on other vehicles and it was the rear and not tranny..good luck...

This is a 4 wheel drive and it crossed my mind that it may be in the rear end. It whines as you accelerate throught first, second and third gear. It really isn't that noticable in 4th, however, that could be due to the increased speed and other road noise. The noise also goes up as the rpm's increase and drops again when the gear changes. The whine is much less noticeable when at a constant speed. Most prominent when accelerating.

When was the last time you checked the level of and replaced the transfer case oil and rear differential oil.

Once you verify that the problem/sound is in the transmission, if it is, the best thing you can do would to bring it to a reputible shop for a diagnosis. A whine can be quite a few things from small annoyances to something a bit more major such as bad/worn seals in a pump. It really isn't that much work to swap out a tranny if you have the proper tools and time and it will save you a few bucks. Plus, if it is the tranny, you can always opt for a better built (then stock) one from a good rebuilder.
The first step though is to isolate the sounds, sounds in the drive train carry pretty well.