Well friends .. It was a toilet issue. Just after 2 days of use our powder room toilet began to clog. Trying plunger N stuff didn't work. Thank god it didn't overflow. But we were scared to use upstairs bathrooms too.
When the plumber came the next day he tried to flush whatever it was. He started to flush from upstairs bathroom and had to use the hose that went all the way up to the basement plumbing before it could reach the blockage. It was something hard like concrete or stone etc. So long story short, his guess was something might have fell down in the plumbing pipes in the construction process. And then I remembered that after our plumbing was done those pipes in the basement was not covered with plastic plates for like a week or so. That time I had to remind our PM to covet it asap.
After this my ever restless soul was still not sure that everything is alright. So we did the snake plumbing sewer camera inspection. And it didn't show anything in the pipes this time.
All is well now !!