I have used the sine wave function up and down slowly from 80Hz and no issues occur at volume set to 75. Makes furniture and the closest 5200 rattle (the chassis not the cones) but not the DSW. So very curious.

Further investigation shows that the Bluray HD version of Alita is fine - the soundtrack is DTS-MA HD. The 4k Bluray disc is Dolby Atmos and my Oppo decodes the Dolby TruHD soundtrack to PCM (as the standard Bluray decodes to PCM from DTS-MA HD). A 4k streaming version via Disney on my Sky box also does not show the issue but then I guess the stream doesn't have the same bandwidth for the soundtrack.

Am I right in thinking the 4k disc has more bandwidth and there is maybe something in it that the Oppo/861/DSW can't cope with?

Regards
Bob

861v8, UHD722v2, 5200s, 5200HCSEup, M6s, 3200s, DSW, Sony 55A95L, Oppo 203, Sky Q Silver
Samsung QE43Q65B, Oppo 105 & Sky Q Mini