I have a Automatic 96 SR5 238k miles. It has been making a high pitch sound (whine) in 2nd gear or when over drive is off which I assume is the same gear. It only makes the noise when on the gas and goes away as soon as you lift off the gas. I have searched many threads and have found nothing about a 2nd gear or any gear specific whine under load problem. I recently changed all diff oils and greased the entire driveline. The ATF level is good and I am about to flush that system soon. Anyone have an idea what this could be from?

My best guess is torque converter.

Mine used to whine in 1, 2 and lesser in 3 while accelerating, could hear slightly in OD at a steady speed.

I dropped pan, changed filter, had some metal residue buildup yet had been about 100K since last one (yeah I know what too long, won't do that again).

So about 6 quarts were replaced with Maxlife. Noise was still there after yet continued driving it and after about 2K the noises slowly died down and are now hardly noticeable. I know nothing lasts forever and that was a warning of what's to come yet for now, all is very good, no slipping (never was) and gently firm shifts up and smooth ones down. Luck.

Will be flushing the ATF and changing the filter this weekend so hopefully that helps. I just ran it up to 80mph with the rear wheels in the air and it does not make the noise. Also it seems to be making the noise in all gears now when it's given more then half throttle above 2500rpm's when in over drive it being much quieter. Sounds like a pulley or roller to me but shouldn't it make the noise with the car in park and revving it if that was the case? But it does not. There is no sign of slippage or lack of normal acceleration. Also with the rear wheels up in the air there seems to be about an inch of play when spinning (turning) one wheel before the other wheel starts spinning the other way. Is that inch of play normal?

The play is normal. It’s the backlash in the rear diff which has to be there for the rear diff to operate properly.

I would also verify your universals are all greased up and are without ply. As they can get noisey when one is going to fail. Mostly they produce vibration as well before failure.

Nothing wrong with exchanging your fluid cleaning the magnets and changing your filter. Automatic transmission love clean lubercating fluid and a clean filter as the fluid can flow properly..

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Since this sound has gotten a little bit louder now I can now faintly hear it while revving the engine in neutral. It also seems to be much louder when the passenger window is rolled down especially when driving. I would imagine its gotta be a pulley or the power steering pump. I changed the timing belt about 60k ago also changing the rollers. Again it makes a high pitch whine when underload from 2200 rpms onward the pitch changes too the more gas you give it. Can't wait to get this sorted super annoying, just glad the transmission should be out of the question now pheeew.

Finally figured this out. Was a pinhole in the muffler whistling.

Thanks for the follow up. Always nice to get a definitive root cause.