Please recommand a free antivirus software with these features

Hi, all:

I have been using Antivir Premium for almost a year. My license is going to expire soon. And I kinda want to try something new and free. I am looking for a free antivirus software with most features that Antivir P has to offer.

The features I care the most probably is the ability to set handling virus alerts automatically and disable alert sounds. Basically, I want an antivirus software does the work without interrupting me. And one more thing, I hope the software is as light on resource as possible.

Thanks