For me it also occurs when I shut off the DAC before my amps. I hate this so I always turn off the amps first now.
I have no issue with Spotify. However, does your own collection in Foobar have tracks with a mix of sampling rates and/or bit-depth? I'm also using the XLR outputs by the way.
Another annoyance I have with it is when I'm say watching Netflix from my PS4 (sound via optical directly to DAC), and it has occasionally occurred that I hear the same crackle/static mid watching, which can occur when my 2.4GHz WiFi gets heavy traffic and Netflix then auto-downgrades the video and audio (say lower sample rate and/or bit depth, basically a lower quality stream), which in turn triggers the DAC to crackle/static at that moment.
So yeah, I hope
@SMSL-Mandy and the SMSL crew have this issue fixed for the successor SU-8S DAC, otherwise, I can't recommend this product as long as it has this issue.