Thank you all for your message. I actually let the Acura Service Center in my town fix my car and now it is running great without any rattling noise. Parts were around $250 and labor was around $260 (higher than parts!! always does..) so the total with the tax was like $545.00. It seemed like they did not charge for diagnostic (which was around $60.00) but if I didn't fix it there they probably did...
Yea, I actually did change my serpentine belt on my own DYI for the first time but when I DYI that earlier this week, it was kind of dark outside so I might have not installed it correctly because when I drove to test to see if car is running ok, I heard some other noise inside the engine bay so I popped my hood and found that my new serpentine belt that I installed got shredded a little bit on the side..
so on the next day, I tried to figure it out why...and finally fixed it (belt wasn't aligned correctly on the bottom left pulley thing) so its belt wasn't no longer moving to the left side when started my car so no longer shredded.
However, since I had the same belt on my car (that got shredded on the side), I think Acura Service center recommended me them to change it...wasted money there but oh well..