engine knocking??!!

Hi,

I am a poor college student and am in need to help desperately! Yesterday my engine started a knock from the top of the engine. Immediately i turned the engine off to save a potentially hazardous situation. I went ahead and changed the oil and put in higher octane, but neither worked. I had a friend listen to the car and he said that it was probably a rocker arm. I pulled the cover off and lifted the cams. I checked out each rocker arm, but they all checked out ok. Looked pretty good. The engine does have 99K on it, but ive treated it very well since having. Does anyone have any ideas on what it could be?

THank you

Aaron Henry

lifter tick a bunch of threads bout it check the eclipse board too theres more people there