Hi Tommy. Hope it is cooler in Metairie. Wish we'd known about this before you pulled the transmission...but from here I'd guess it is the input shaft bushing. Although it possibly could be the throwout bearing. One way to check these is to push the clutch in all the way, keep it down and then shift into neutral. If the noise continues, the throwout bearing is failing. If the noise stops, the source is the input shaft bushing (and I will tell you why in just a moment). However the throwout bearing makes a sound all its own.
Why do I say it stops when the clutch is in? When the bushing wears as you've described, it lets the input shaft move around in an "off-center" manner...I don't mean to say it bounces around all the time, but when you shift into fifth it can stop moving anywhere when you let the clutch out. At times it may be centered and at times it definitely won't be. And this will cause the shaft to wobble around some inside the transmission and when it does you can and eventually will get all sorts of weird noises. I always noticed it more in the top gear and I decided it was because that gear can have less acceleration stress on it at times and it is at those times it will start howling and whining the most. Once it starts I think it is normal to let off the gas and listen and that can actually make it howl a little more. When you push in the clutch, you free the shaft and it no longer is running in that same "wobble" pattern. So the noise will stop.
The good news is those are cheap and easy to replace.
