Sound System Does Not Sound Good from Laptop

Hi.... I need to ask how to configure my laptop sound system. It is using Realtek High Definiion Audio (laptop showing Altec Lansing brand at the keyboard). Anyway, when I put it to the loudest, it sounded cracking and difficult to hear. I thought with Altec Lansing sound system, it should sound really good and loud.
Appreciate if you could advise me the right setting for my Asus laptop. I just bought it about a week ago.

Thanks.