Static pop sound in the beginning of every track - Violectric V200

[kodreaming]

I got an used V200 with USB Dac recently. I have tried two different USB cables with two different Macbook Pro. But, there are always a couple of light static pop sound at the beginning of every track. I tried both Vox playing local files and Spotify.  I tried with three different headphones and they all have this problem...
 
It only happens before the track starts but never during the track...I know the problem is not with the Amp part since I tried it with an external DAC.
 
Thanks...