Nose shake

I don’t know why this is, but for many aircraft when I approach cruising altitude, the aircraft nose begins to dive and climb randomly. For example, if I’m cruising at 30000 feet, the nose will continue moving up and down and then plane will go between 29800 feet and 32200 feet. Just wondering why this happens?

There was a similar problem here.

This is happening to me also so don’t feel alone