Hello, i have a problem with my macbook pro mid 2010. i have macos sierra on it 10 gb of ram and 120 ssd aluminium model and everything works fine . but the microphone isnt working . it shows up in the system pref but the volume bars are not moving . but , when i hit the laptop in the bottom left part with my fingers the volume bars start to show up but in a grey colour. as i said the bars show up only when i hit the laptop , i tried to speak how loud i can but ive got no answer from my mic . thank you