Grinding noise/feeling around 6000rpm

[Chris]

I know you say it's connected to engine speed but is it anything to do with the road speed? Possibly the wheel bearings as they can be worse at certain speeds/load.

One thing to be careful of is that sometimes the markers on the rear swing arm can be a bit misleading and even if they're set the same the wheel can be slightly out of line but I'm sure you'd feel that through the steering and behaviour of the bike. Might be worth checking another way to make sure the wheels are dead straight. If they have been out of line then this can put extra strain on lots of things but might contribute to the bearings wearing out faster.

Hope that makes sense.

chris