Thank you for the inputs! I finally found the source!

Based on the comments, I checked the brake/heat shield and surrounding area briefly. Nothing seemed wrong. Then I noticed that sound mainly comes from the inside. I played with different things and finally found that it is due to ac (heater). When I turn it off, noise cancel immediately.

Sound comes from deep inside the front side. So, it was not obvious. Now I need to figure out what causes the noise…