Laptop surface vibrating when rubbing over it
Yes, the lack of grounding might be a reason. 

If there is an X capacitor internally it can cause a current flow that is large enough to be perceptible. 

If, where you are, your power has one pin 'hot' wrt ground and the other 'neutral' wrt ground, as well as a non-polarized plug/receptacle, you can try reversing the power pins and see if it goes away.