I'll throw in a few tidbits. I'm familiar with the OD. Not sure about the tranny since never took one apart.

First, How is the fluid level? When was the last time the fluid was changed? Straight 30W oil or type F transmission fluid. NOT Dextron.

You have no or (not noticable?) noise in first and reverse, increases in noise with increase in speed with 2-4 then drops with OD use.

Based upon bearing noise, if it is in tranny, I'll take stabs which will require others to assist in some areas with clarification.

In the OD there is a bearing that rotates in R and 1to4 but not in OD mode. When OD is engaged, this bearing stops spinning so any noise it makes will stop, not reduce. This eliminates that bearing as making noise. The other two bearings in OD mode will increase in RPM since the OD increases output (driveshaft) RPM while reducing input (trans) RPM. Since noise is reduced in OD mode, noise is most certainly comming forward og the OD.

Tranny: Need help here...

How does 1st and reverse gears and synchros interact that is different in 2 through 4? I do not know so somebody else fill in the missing info.

Throwout bearing?? Pushing in the clutch will do nothing for noise since the bearing is still being spun by the transmission.

Does riding the clutch change the noise?? If it does, adjust the clutch cable free play first. Then it might be time for a new cluch* and throw out bearing.

At some point you will have to drop the tranny to get whatever fixed. *If it is off, best time to change to new clutch and pressure plate. Saves dropping the trans a second time.

If you have a second vehicle, drop the tranny and check out the throw out bearing first thing. If it is bad you will know immediately.

Look from easy/cheapest to hardest/expensive as a repair process.

Duane