Transmission whine 4th gear overun

My GRiSO whines on the overun in 4th gear only.
Sometimes (especially if i am close to a reflecting surface like other traffic or a wall) it is audible with a full face helmet

-but it is more obvious when wearing an open face helmet.  Over 10,000 miles I don't think it is getting worse - just i am getting more used to the bike and hearing things better.  

The oil comes out slightly grey and metally like i recall most Guzzi gearbox oil.

Any expert opinions please??

Jon

My gearbox oil is always clean and clear after 150,000 km. Something is wrong.

Do you drain the oil after warming it up by riding? If so it's probably just aerated. If it's actually got silver crap in it it needs investigating. The Nuovo Six Speed is an incredibly tough box. I've yet to have to repair one that has actually broken.

No metal bits on the drain plug or visible in the oil stream just fine metallic sheen (not metalflake) in the oil.

Will photograph the colour / transparency at the next 6000 mile service

My oil changing routine involves a 15km ride to warm up the fluids. Then I drain the gearbox and carc, let it cool a little more and drain the engine. My tansmission fluid is always completely silver looking and I freaked out the first time.

Let the bike sit overnight and try opening the drain plug to let some oil out. If it's like mine, it will come out the same color as in the bottle After all, the drivetrain is an excellent air-oil blender.

edit: now that I think about it more, if you are afraid to have an issue with the drivetrain, you might not want to wait 6k miles to check. It would be better to actually go for a ride and check if your oil is silvery again, then wait overnight and check the color again.