Yes, I know they're from camera shake. It was so windy that hanging a bag from the hook at the bottom of the center of the tripod would've have helped because the bag would've just swung back and forth in the wind. The auto shutter delay is a good tip. I'll have to look for it in the menus.
Yeah, I noticed that the D3400 doesn't have exposure bracketing. But it's ok because I can use my tripod to take two or more exposure of the same frame.
Thank you for your comments!