[Anechoic]

I wish there were an expert or researcher interested in these areas: residential buildings, shops, parks, churches, and schools.

You mean an expert in acoustics related to those areas? There are lots of experts and researchers. Take a look at the Acoustical Society of America, the Institute of Noise Control Engineering, and Council for Accreditation in Occupational Hearing Conservation for starters.

Penn State, University of Hartford, Purdue University, Michigan Technological University, University of Nebraska, Morgan State Univeristy, and Brigham Young University (among others) all have strong acoustics programs with research in a bunch of areas.

[todotask2]

Oh, but I'm in Singapore.

[Anechoic]

https://acousticssingapore.com might have some leads.

[leakycap]

That might make you want to look at that list of organizations and then seek similar organizations or schools in Singapore, if you didn't already try. Good luck with the hum.