Crackle noise is probably the relay. Hissy noise is probably the DAC… at least that is how it all panned out my fixing my unit.
When my relay died, I called Omron and they told me to use this part as an exact replacement
653-G5V-2-DC5
Omron Relays - Low-
DPDT PCB 5VDC
and it worked.
best - DT