No one is totally sure why this is happening, but some Reddit users have theorized that the phenomenon is caused by “uncapped unlimited frame rates” on loading screens. This has happened before, most notably with Rainbow Six Siege. In Siege some players have shown their framerate jumping up to 999 frames per second during loading screens, putting extreme load on their GPUs. The frame rate then drops to a more reasonable 150 FPS once matches actually start. The solution has been to cap the game’s frame rate on a system level to avoid straining the GPU during loading screens. Sadly, PS5 Deathloop players do not have this option.
I tested this theory using my own PC build of the game (where the game has a whole other set of problems), and it seems sound. Disabling the system wide framerate cap I have set on my PC, and entering any Deathloop loading screen, sees the framerate skyrocket to 400+ frames per second, at which point my GPU starts shouting. Once I’ve managed to load in-game, the frame rate drops to a more sensible 60-80 FPS and the shouting abates. Re-enabling my precious framerate cap sees much more reasonable frame rates on loading screens, and a happy GPU.
While some users aren’t too concerned about the sound, on account of it only lasting a few seconds and not being a problem anywhere else, I think that the peace of mind provided by your console not making a new and terrible noise is well worth the effort of fixing.