Metal-on-metal rasping cicada-like noise

Hi everyone,
Anyone ever run into this kind of noise?
2013 Prius+ (Prius v for USA/Canada)

When I accelerate gently while on the gas engine, I often get this weird metal-on-metal rasping / grinding noise a bit like a metal cicada or like a saw against a metal bar. Goes grinn-grinn-grinn, sometimes once, sometimes a few times in a row.

Toyota said everything looked fine at service. Took a mechanic out for a drive — he heard it too but had no idea. Appointment booked to dig into it.

Short recordings (hosted on my PCloud) will be posted as soon as am given permission (but I should post 4 times , so quite hopeless.)

 

Copy paste error
The message should've ended with :

"Appreciate any thoughts or ideas.
Thanks!"