It's probably caused by the sound of digital distortion, I think you might turn volume too high. Make sure you get a good signal and a decent level.
Or I think it also can be the signal distortion due to the different sampling rate that your sequencer and sound card have set. e.g. sound card is set to be at 44.1KHz and sequencer's set at 48KHz.
I am sorry mate, I don't want to write in English as well, but I haven't got Chinese Input at moment, I will write Chinese as soon as I have it. sorry for that.