xLEGENDx

Hello, the short version of the dumb question is, is the transfer case "working" when the transmission is in P or N?

the long version: I had to drive about 500-600 miles with atf in my transfer case, which afaik is thinner than the recommended 80w-90. The car makes a whiny/humming noise and I am aware of the long list of reasons that can cause whining on these cars but I would absolutely love to exclude the transfer case and think that it is just a coincidence The noise can not be heard when the car is cold, neither when I let it warm idling in P, but it can be heard clearly after I drive for some minutes, then the noise level is the same in all gears, P R N D and it is not changing with revs, also cant be heard while driving.
here is the recording in my garage:
noise

I would love to hear some advices as I do not live in US and outside of US these cars are almost exotic, so maybe even some Acura/Honda dealers don't have as much experience with them, as most users here on this forum

Blues Legend

The transfer case is merely a 90 degree hypoid bevel drive; it is turning when the propshaft is turning, so will obviously be silent at stationery and the resonances will increase with vehicle speed.

Since it is a bevel drive, the shear loadings will break down the oil polymers very quickly which is why it must be run with an EP oil with sulphur additives (it smells bad) and not ATF.

Put the correct grade EP oil (available from any Honda dealer) in immediately before you do any further gear damage.