Hi @li yu,
Thank you for the additional info.
The reason why you're getting the crackling sound is because you're not applying 48V phantom power to the microphone when connecting the 3Dio to the Scarlett using XLR cables. 3Dio microphones are like most studio condenser microphones in that they require phantom power in order to properly function (when using the XLR outputs).
The battery inside the 3Dio only applies to the 3.5mm output and does not power the capsules when using the XLR jacks. The battery allows for remote recording for outdoor use or whenever a phantom power source is unavailable.
My guess is that you had to increase the volume/gain settings on your device in order to get any audio from the XLR outputs, correct? Once you enable the phantom power on the Scarlett, the audio output of the mic should be much louder without any crackling noises.
Give this a try and let us know if that doesn't resolve the issue.
Best regards,
~Brian
3Dio Customer Care