High-pitched whining/rattle when accelerating past 15 or 20mph

[Louder North]

I took a piece of 180 grit to the clutch pads and scuffed off the black stuff.
Cleaned the rollers and all components.
I put the belt back on so that the writing is right side up.
Still makes the high pitched sounds. At around 20mph.

The bearing that's visible when you look in to the clutch/drive pulley assembly, that bearing needs replaced. I'm fairly certain that it's the culprit.

Did you check the oil level in the final drive? 

If the bearing is gone, you can quickly check for any side to side movement in the rear tire (there shouldn't be any or very little) when the scoot is on its center stand.

[Stig / Major Tom]

You might find  it helpful to own a service manual for your scooter.
One is available for your model here:

https://www.repairmanual.com/product/kymco-people-150-125-scooter-service-manual-printed-by-cyclepedia/

The price of this manual represents about 15 mins. of labor time at your local scooter shop.


Stig