Hello everybody , I just finished my gearbox and installed it , it makes a kind of whine on 3-5 gears , it’s almost inaudible , thankfully the camera catches it . I don’t have any issues with the sound it’s almost impossible to notice unless you know when to listen . I am just concerned on if it might be something I can fix , or if it may give up without warning . It is noticed when foot is taken off the gas

Here is a vid : https://youtu.be/01goQwgHWoI

I'd drive her, that being said I would put a magnetic drain plug in the filler hole and watch for metal flakes. Not making a lot of noise, they can get much louder.

I have installed a magnetic drain , previously the input shaft bearing was destroyed so it must have produced many flakes , also the first gear digteeth where destroyed so more flakes there , also the input shaft bearing cage produced copper flakes in the oil , I cleaned the parts but surely some of it remained , so I have some flakes on the drain but not anything extreme . Now it runs with a new input shaft bearing and first gear teeth .
My concern is what might cause this sound and if it’s dangerous for the gearbox . Or if it will warn me in time to repair . Also I am wondering what kind of life it has in it

I would watch closely for more flaking. If it is causing more flaking it will ruin your new bearing.

Thanks for your answer
How Much flaking is acceptable ?
What do you think it that noise ?