Weird problem with VN - Grinding / Freespinning noise

[Defected]

Series 1 VN Commodore
When the wheels spin up in the wet or dry and it hits about 4100rpm there is a grinding /whirring noise almost as if something is free spinning and a lose all power until it bogs back down to about 2800rpm

any ideas?

[DavoVP]

Gear box ?

[Defected]

i thought it may have been.
Note the right rear axle seal is in need of a replacement.. could it be that?

[havavb]

When i put my foot down after stopping the rear left wheel (Im guessing Bracing or something) grinds really bad. But i dont loose power. Do we have the same problem or different problem?