noise is fickle...
- it could be interference from the router as
@Jimrahbe suggested (try moving the transceiver away)
- it could be noise from other electronics (tv, stereo, roku/firestick/streamer, lighting, nearby switch-mode power supply/adapter etc.)
- it could be a problem with the transceiver's power supply (i believe the wireless link ships with a switch-mode supply)
- it could be a problem with the transceiver itself OR the protocol adapter
You said the noise stops when you unplug the transceiver... does it stop if you leave the transceiver plugged in, but disconnect the 4-conductor cable between the transceiver and the protocol adapter?
if jim's suggestion and unplugging the protocol adapter don't work, try another 12v power supply... just make sure you use a positive-tip supply that's rated for at least 500mA (the tip orientation and output current should be marked on the unit)