voice distortion

I recently purchased an Inspirion 1520 Laptop from Dubai. The problem I am facing is that, whenever I am talking to someone over VoIP through a headset or without headset my voice is getting massively distorted and is sounding like when someone speaks with an empty pot or bucket on their mouth. it is very heavy, somewhat robotic voice. I think the problem is with the inbuilt speaker of this laptop. Can anyone help me in this regard? Help is needed urgently.

Thanks so much.