I think I have found my problem, my GPU was actually running at 100% all the time. Even on idle. The fan didn't run at 100% speed though, it was more like 20% speed so I neglected it throughout the week.
It was until tonight. I was checking my ATI overdrive settings then I saw it at 100% activity. I think this problem started happening ever since I installed Firefox 4 (I mentioned I didn't installed any new software in the original post but I didn't think a browser could have caused this). I've looked around and some people are having the same issues (no mentioning of any delays though). They believe it has something to do with hardware acceleration on Firefox 4. Right now, I am temporary using IE8 and no problems yet. No delays, GPU at 0% on idle. So far so good... Will roll back to Firefox 3.6 tomorrow and test it out.
UPDATE: Firefox 3.6 works fine for me.
