I have this strange issue with my OSSC and the Sega saturn, whenever a game is using streaming cd audio.
For example, Mortal Kombat 2 and UMK3. After boot-up, you get a few screens with various logos, copyrights screens, and then the logo, but when you reach the game mode selection screen, the game starts playing a little drum background track and thats when the hissing starts happening.
I tried it with several saturns, jpn and american editions, and the hissing is always there. I also tried it with another tv.
The only other cd-based consoles I have on this setup are a dreamcast and ps2, but they didnt do any hissing, but I highly doubt that those games were streaming cdda tracks, it had to be all compressed tracks in mp3-like formats by the time those consoles were released.
I tried with different scart cables, including no-names ebay cheapies and high end stuff from retrogaming-cablesuk
It really only happens with games that happen to use cdda music track, as far as i can see.
It’s not SUPER annoying but it’s very noticeable, especially when playing at high volume.