Noise when shutting down engine

[YoKr]

Hi everyone, I'm new here.

I own Yaris 2012 (Sol) for about 2 months.
Last week I've first start wondering about the +/- buttons behind the steering wheel and figure it is the manual transmissions control (Using the car manual too).
Mention I've pressed these buttons several times before switching to manual mode until I figured it up.
Consequently or not, when shutting down the engine every time since that day I hear (from the car front, driver side) some kind of a weak buzzing/rattling noise, for a 1-2 sec and disappear.

What are your suggestions and shell I be worried?

Thanks in advance,
Yoav