Core X Chroma – Fan Overload During iMac Sleep

Morning, Handsome Nerds! I have a problem I know you can fix. My (excellent) Core X Chroma with a Radeon VII installed is spinning up _hardcore_ every time the iMac goes to sleep. It's a bit of a drag, really: I suck enough power as it is, and I'd really appreciate being able to shut down the screens and leave it running. Any ideas? Thanks so much, T