Default Haptic feeling when tapping at the upper back part

hi guys,

does anyone noticed that there is a slight haptic feedback feeling when you tap the back part of your note 3?

I have an S3, but when i tap it at the back. it doesnt create a haptic feedback effect.

i just got the unit a week ago and i just noticed it a week ago.

tried to search for a similar thread or anywhere. cant find anything. hope someone can help me on this or am i just way too sensitive.

thanx