@chloe-zhao -thanks for the response.
Yes- I tried changing to HDMI 2
No - I can't download the audio sources, but it can be re-created easily:
1 - plugin either an ipad pro and play movies from iTunes, or
2 - plugin an amazon UHD fire stick and play any movies - with the audio set to anything by stereo
3 - plugin any generation of apply tv and play a movie
All have the same effect and the audio is just crackles, hisses and pops.
Thanks
Dave