This applies to the Audio/Digital Card for Legacy Platinum Preamps
This is most likely to be a sync problem so the first thing to check is that the sample frequency and bit depth are set to the same for the Platinum ADC card and for the receiving device.
The Platinum ADC cards output a 24-bit digital signal and the sample frequency is selected using the buttons on card itself (or on the front of the unit on the Octopre and Octopre LE). The next thing to check is that the clock source for the receiving device is set to S/PDIF input. This is all you need to set to ensure you can get audio digitally from the ADC card to your receiving device so if you are still experiencing problems then the next thing to do is:
-Check that the noise does not appear on the analogue output of the Focusrite unit to ensure that this is a digital card issue.
-Try to see if the problem is heat related - does the noise occur after the unit has been on for quite a while or does it occur straight away when you turn the unit on?
-Try the unit with a different receiving device with a S/PDIF input to see if you get the same results. This will let you know if the problem is with the ADC card or not.