Hello,

I think the best advice has come from CB posts!
It's time to spend some time down below.
Looking into its blood drainage is a first step.

A whirling sound, in neutral position, is most likely one of the two front input shaft bearings. These are two bearings that do "turn all the time" at engine speed even in neutral.

A throw out bearing can make a noise when the clutch is depressed. Otherwise, that should not be turning unless there is no play between it and the clutch arm. The whole affair spins as a unit.

Do you have some free play at the beginning of the throw on the clutch pedal? I think there is suppose to be one inch up there and about one fourth of that below.


The weird part about this is that it's coming and going. More so, involving slowing down ... without shifting problems.
How does the shift lever present a feel of vibrations?
Have you held onto the shift levers base with your finger tips?
Pushing the lever for each gear, with the play in it held at either end lightly, holds the gear shift fingers play in one direction.
Do you feel any rumble through it as it sounds off?

With that said, I think CB is right to advise you to look closely elsewhere and working with his idea, it might be flowing towards some bad-u-joints!
Have they ever been changed out?

I have some that old on my cars and I check them fairly regularly because I have a car lift that makes it an easier routine.
That doesn't mean I won't have a failure as those needle bearing do not spin around. They will get rusty and crunchy working back forth in a short arc of rotation distance. I don't unbolt my driveshaft routinely and truly feel them out. I'm not anal but I do stock the joints though.

Slowing down and a snap change of direction upsets the apple cart with them needles bearings! They can be Fine one day, then Bam, they can cry out or fall out! The noise after that, I will say, must be indescribable!

The can of marbles it awful unnerving, in context to precision device and a transmission definitely is that!
It's the coming and going that haunts me on this. Expect shorter intervals to be on the horizon, if it's transmission?
So with it moving on to second and third gears the bearings may be losing some thrust handling capability. An inducement from the driveshaft might get to the tail shaft bearing.
Is a rear seal weeping a bit too much?

Keep us posted, as you have interesting subject of symptoms.

Phil