Folks, here are some general tips in the iGalvanic3.0 case:
1) Use known good cables of correct specification. Generally speaking, those included with iFi products and / or good grade generics will be correct, but many audiophile cables are not correct in terms of specification.
2) Make all connections to iG3 and set the earth link switch as required. Make sure that the port chosen on the source is a fully USB standard compliant port.
3) Make the connection to the Source (PC, Mac etc.). Remember that USB negotiations and enabling/updating drivers etc. may take up 30+ seconds before a new device is operational after connection.
4) In most operating systems, the attached DAC will show up as a new device. So it may be necessary to re-set the audio configuration of the machine, of playback software etc.
5) Take your time, don't rush things and act systematically in tracing and correcting faults.
In addition, proper iGalvanic3.0 operation can't be guaranteed if this product is connected to a socket which isn't USB compliant. The same story is when one or both sides of the system float without earth connection. Earth Link switch set correctly is there to ensure reliable (or any) connection.