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