The pedal also pulsated.
With the windows closed on the cold weather, it was diffecult to locate the source of sound. I felt the the sound was from wheels.

I guess the ABS functioned, anyway.
The road was splippery due to snow: when I pressed accelerator pedal, the whole car body tended to spin due to real wheel slip. But when I pressed brake pedal, car body did not spin - probably ABS successfully prevented the wheels from locking -.