I was doing tie rods today and noticed a pretty significant noise coming from inside the transmission when I rotate the passenger side axle by hand. It seems like there's a bit of 'free play' before it engages, but no play after that. If I go from forward rotation to reverse, it always clunks. Is this normal or does anyone have any insight as to what this is? I'm praying my transmission isn't on the way out...fluid was changed by me at 125,000km (now at 168) with an approved fluid from Amsoil and the current ATF level is in spec. No noise when I'm driving/starting/stopping that I can hear. I can only detect this when rotating it by hand.

Edit: I was initially thinking that the axle needs replacement, but there is no play in the axle itself as far as I can tell.

Video: