A squeal or a hiss. Or a shuddery sound. By all accounts something is amiss.

I would take it apart ad see if everything looks proper. If it looks good, use some special sprinkler grease and see what happens. Might get a rebuild kit just because. Could also be a valve not totally closing and you have a small amount of water still flowing through the valve. That can make funny sounds. The beauty of sprinkler parts is they have the shelf like of yogurt. I had to replace a valve this year. A different on last year. A few heads the year before. Good thing sprinkler parts are cheap.

Two years ago I started removing my back flow device and taking it inside. Draining and blowing out didn't work a couple times. So now I take the whole thing inside.