My Nismo was 2 way when i got it but i got it adjusted to 1.5 way, the housings on the Nismo and Cusco (I assume selected models) can be rotated to change the ramps etc.....
The noise you describe mark is kind of what i had when i put the solid locking rings in the rear, it went away when i changed my diff so i can only assume one of the axle bearings in the diff were shot?
As for the shudder on launch that sounds like axle tramp? Mine went away when i did the locking rings etc (mostly anyway)