Just started to get the same problem. No change in recent configuration. Continues with different DACs (Meridian explorer, Meridian prime, audioquest dragonfly) fed by USB from MacPro running 10.10.3 and latest Sooloos software from C15 with TwinStore using desktop audio. No difference with 16/44.1 or 24/96 FLAC files. Seems to increase in intensity as music is louder. It does not occur with C15 into non-desktop system. It makes desktop listening impossible.

Ross.

Control:15, TwinStore 2GB*2, 500, Auralic Vega, Pass XA60.8 x2, B&W 802D, Stax lambda & SRM-T1S, Prime Headphone Amp., HiFiMan 500