I started my Evo 8 this morning and suddenly, the engine starts to knock. I also notice when I opened my oil cap, there are some white stuff mixed with my oil. Can anybody tell me what the white stuff is and what can be causing it?

 

Does it look milky white like chocolate milk? If so you are noticing what happens when a head gasket blows. A portion of the gasket keeping the oil in the oil passages and the coolant in the coolant passages gives way and allows coolant to mix with oil and that's the effect. Open the cap, take a picture and post it up but do not drive it. Coolant doesn't lubricate as well as oil does

 

Coolant in your engine oil which sounds to have killed a bearing.

 

If it looks like Choc milk it's not good, As said already could've spun a bearing. When was your last oil change and who did it. Also the weather hit single digits could just that also. But if it's knocking sorry to hear, Looks like it's time for a New Engine............

 

Looks like you have your answer. Then keep in mind your Evo is a 03.