High pitch whine when accelerating

[cheapeto]

I was riding this past weekend with a bunch of rucks,groms,zuma's, I think it was a zuma 50 that when coming to a stop, or on the hard decelarations you do going down mountain roads,working the hairpins.
It would whine down.
The groms were absoluty awsome machines!!
If I was a younger man, this would be my choice for a small motorcycle as I do miss the gear changing at times.