I opened the hood and noticed that cooler is kinda shaking. a/c was on while capturing. I'm just wondering if it's a normal noise from engine.

 

Going to move you to the Stock Problems/Issues area. My ears are not the best but I thought I did hear some clunking on the belt side. Below is a link to a recent post where a person has a good auto "stethoscope" idea. It is the sixth post.

How many miles on the car? Are you aware of whether the belt tensioner has been replaced or any idler pullies?

https://www.northamericanmotoring.co...from-hell.html

 

I currently replaced harmonic balancer but not sure if mechanic changed the belt as well. it ran 85k. 2003 mini cooper s

 

Belt tensioner could be the issue.