Severe short term audio distortion when watching Netflix

Hi all , I can't find a reason for this anywhere - so posting as widely as possible

My Setup

New Win 10 PC with Matrix Element H USB card - Sablon 2020 cable to May KTE DAC - handmade Silver XLR's to Hegel H390 to Dynaudio Heritage Specials

For the last 12 nights, while watching Netflix or Youtube - the audio is swamped by severe high pitched distortion for 3-4 seconds , then all returns to normal

This only happens once per night - between 7 -10PM. Only once, never during the day and only for 3-4 seconds - all was good for more than the last 12 months with this current setup

I have contacted my internet provider - all is good from their end - have checked with a speed test as soon as distortion starts and speed is normal

I have replaced the Ethernet cable

I have uninstalled and reinstalled the Holo Audio driver for my MAY KTE DAC - on a suggestion from Microsoft Support

I have rebooted  PC several times and switched off May DAC and unplugged power cord for 30 seconds

Any ideas or suggestions appreciated

Michael