My beloved pickup, Helga, is making some transmission noises these days that are gradually getting worse. She’s a 4x4 and has about 182k miles, which is pretty young for a Tacoma. The transmission fluid was changed about 10k miles ago, as well as the clutch fluid and both diff fluids. This is the scenario in which she starts grinding:
-in any gear
-clutch pedal pressed
-truck is rolling
-grind is definitely related to rolling speed, not RPM
-sometimes, it doesn’t happen when clutch pedal is pressed, but does happen when I downshift. Stops when I let off the clutch.
-I don’t ever notice grinding when I’m shifting up the gears in acceleration, except sometimes if I keep the clutch pedal pressed with trans in gear for an extended period of time (for a shift, like more than a couple seconds).
I’m not having any problems with shifting or popping out of gear, etc. Other than the grind, the transmission seems to be operating just fine. Help me nurse Helga back to health. Thanks!
Does the grinding stop if you shift into neutral, keeping the clutch pressed?
Yes, it stops if I shift out of gear but keep the clutch pressed.
Then you might have a bearing going out in the transmission. If that’s confirmed, I might look for a used one from a recycler/junkyard.
you should of fell in love with Helga’s younger sister. LOL
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Dang, I hope that’s not it. I’ll see if I can put her on a lift and confirm that.
Hahaha yeah maybe. Would like her to be a little bigger, with 4 doors 
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Is the grinding noise accompanied by hard shifting? Is it acting like the clutch is not fully disengaged?
(I am surprised about how the clutch changes the noise. Does the noise happen in any particular shift, or gear?
When your truck is rolling, in gear, and the clutch pedal is depressed the gears inside the transmission are being driven from the final drive gear, from the rear towards the front, to the trans input shaft. When the clutch pedal is out the gears are driven from front to rear. So maybe something to do with that; i.e. play between gears or in trans bearings that only shows up when the gears are driven is from rear to front.
The other possibility is the sound isn’t coming from the trans at all, but from something that is activated only when the clutch pedal is pressed; e.g. the release bearing/mechanism, the pilot bearing, flywheel, crankshaft thrust bearings (since the crankshaft is bolted to the flywheel) , etc. You might try using a mechanics stethoscope w/the vehicle on a lift to see if you can narrow down where exactly the sound is coming from.
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Noise with clutch depressed in gear, no noise with clutch depressed out of gear would seem to indicate noise associated with the trans input shaft, maybe bearings.
It’s not accompanied by hard shifting. Truck shifts fine (a little clunky from 1st to 2nd), but the sound can happen in any gear. Happens in down shifts, but not up shifts.
Do you have to be moving ?
Will it grind sitting still, clutch pressed and transmission in gear ?
Thinking pilot bearing.
Yes I have to be moving. No noise if I’m not rolling. I’m quite certain it’s not the pilot bearing.
If you have to be moving, it’s not the pilot bearing.
I am leaning towards the idea of weak synchronizers. You have described the problem primarily on downshifts, but also on upshifts when done slowly.