High pitch noise on autogear – Subaru Impreza EL15 2009

hi. when driving my car subaru impreza 2009 automatic, i sense a not loud but high pitched noise just before

the gear shifts. i don’t have light indicator on the dashboard what could be the cause for this ?

thanks in advance

Brand: Subaru
Model: Impreza
Year: 2009
Engine: EL15