With passives its almost always earthing. Defo check you're getting good connections with your cables. Also, if it's been moved around a lot and/or plugged/unplugged, might be worth checking inside that nothing has come loose. If you have a multi meter, check all the grounds are connected and that none of the signal lines are earthed (unless the volume is on zero)
SBT/Chromecast/TEAC T1 into TEAC D-T1 DAC or olde-worlde Rega Planar 2 controlled by Rotel RC850 into HH S500D or DACT Passive Pre into Mullard 5-20 monos. Then into Tannoy Cheviots and a Wharfdale sub. All connected by colourful cables.