Maybe it is because 1st/2nd are part(machined from the same piece of metal) of the input shaft?

I know they're not straight cut... I have my stripped spline input shaft sitting on a shelf.

I've only noticed it in first, when I bought my car, after the Sheptrans rebuild and after the recent input shaft replacement. It's just one of those noises that will always be there... like the noise a turbo makes when it's spooled up.

 

Thought my car was the only one, till I drove my friends ix which has only 6k miles. Normal.