RIP, thanks for the reply.
1. Spark plugs are 3-4 y.o. Is it time to replace it?
2. I have not yet started to use A/C. I do not think it is related to A/C...
3. There is no warning message on the main board.
4. Forgot to mention. When I start a car or press gas I can hear the more stronger noise (like B-r-r-r) as usual!
I will change the O2 sensor, of course.
Eugene