Carrera Vengeance e bike whining noise

[Art58]

I get a loud whining/ grating noise when peddling between 8 - 15 mph and taken it back a few times and problem still persists, any ideas what this could be?

 

[Michael Price]

My Carrera crosscity e used to make a whining/screaming sound mostly in high assist - but it had started to do the same in medium assist.
It mainly did it at the higher end of the speed range - clearly came from the motor so it cut out at the cut off speed

I recently had the batter recelled and when I got it back the whining/screaming stopped
I presume it was something to do with the voltage/power being delivered from the battery to the motor and the better cells made it the proper level again.

Lots of people have a better idea of how these work than me so a more informed opinion would be welcome!