Anyone know the reason for this(please check the video below)? gimble acts weirdly.never crashed before.usually fix this after restart. thank you in advance

wow! i have never seen that before!

I think your drone is possessed, have you tried refresh the firmware.

you can calibrate gimble in DJI App. Update new firmware and check again.

Check the flat ribbon cable for breaks or even dents.

I tight the grub screw. Now gimble is completely silent. But the camera works. Tried to calibrate the gimble. But didn't work.

I'm afraid that the issue can not be solved remotely. I sincerely suggest to send it in for a fully diagnosis: https://www.dji.com/support

Mine does the same thing but that was after a crash. I had to replace the gimbal and the main ribbon and now it does this.

You have a bad potentiometer on the roll sensor board. You can replace the whole board or just the potentiometer if you're good at soldering small things.
https://www.youtube.com/watch?v=_01o8r8NbGM&list=PLWI_xRaG_vq-sRavo8NTm0L7MwzRQb1sg&t=63s&index=10