Macbook Pro 15" (Mid-2010) screen flickering problem

Hey guys! New guy here. So as the thread title says, my MBP has a screen flicker problem. I tried searching for examples in youtube so you could see but my case seems different from the others. The screen flicker my MBP has is similar to a screen static whenever a nearby mobile phone is receiving a call/SMS...happening constantly, it doesn't die off. However, when I try to boot into safe mode or plug it into an external display...it doesn't flicker anymore. What does that mean?

The screen flicker problem started when I reinstalled Snow Leopard because my MBP was stuck at the boot screen. Even in the reinstallation, the screen was already flickering.

Really appreciate your inputs on these. Cheers!

Well, I just discovered something. Whenever I untick the Automatic Graphics Switching at the Energy Saver Preferences, the flickering's gone. Does that mean that there's something wrong with the Onboard graphics card (not the Nvidia one)?