2012 Toyota Prius c whining noise

2012 prius makes a high pitch, sounds electrical, whining noise that is coming from the rear side of the transmission. Noise will occur during acceleration (with vehicle in park) and noise also increases with RPM at highway speeds. Does anyone have an idea what might be causing this?

Transmission oil could be low or deteriorating.How long since your last transmission oil service?

Prius has a cvt trans sandwiched between an electric drive motor and engine. Many things that could cause issue. A dealer tech might be aware of common issues. Which may lead to large component swaps via warranty route. No warranty? We owned same car. Gone now.

Thanks for the info, check fluid and found level to be OK. When checking, I found a fastener missing by the plastic cover over the oil filter. Replaced plastic fastener and high pitch vibration sound went away. Who would have guessed that this would produce this sound?