After upgrading to sequoia my monitor periodically turns black

I have Mac Studio (with M2 max processor) with Sequoia 15.1 and after upgrade (from Sonoma) my monitor will randomly turn completely black, approximately every few minutes. When that happens CPU usage of Wallpaper goes to above 100%. As the screen recovers i can see the foreground but the background is black (and CPU usage is now visible in Activity monitor as above 100%). Then when background recovers to uniform teal the CPU usage of wallpaper returns to normal (essentially zero). My wallpaper is just a uniform teal and screensaver is simple standard sequoia.

Also (perhaps coincidentally) the hard disk usage of my back up drive is high as i can hear it furiously moving the head around during this time. but i dont see any process that would indicate a backup process.

Also appears that this blanking will be initiated by selecting apple menu items (may be coincidental).

This is incredibly annoying.