Long time happy user of a Madiface USB connected to an ADI-648.

In the far left section of the ADI-648 front panel there's a switch to select between Optical and BNC MADI input. I've always used optical with nothing connected to the BNC MADI IO.

For some reason recently (can't say I noticed exactly when) this BNC light has begun flashing on/ off even though nothing is connected and all functionality of the whole system is perfectly in sync and performing ideally.

I'm trying to track down why. I had a look in the manual but nothing seemed to relate to it. If it was a sync related light then flashing is mentioned a lot but for for MADI IO connections there's no mention of a flashing state.

Any thoughts on this please?