sudden acceleration on pushing gass

i have a hybrid car ,when i am parking and i switch on car ,the RPM pointer will be first go to 1 RPM to charge the battery then goes down to green area of RPM(electric mode) the queastion is when i sudden push on gass a little bit the RPM goes few seconds to 1 RPM then it produce a small click from engine then return to green area .is this click normal?from wer it is?this thing is somtimes not happen always.please help and thanks for your patience