I am an associate lecturer and its my second term with the undergraduate students.

I noticed some of my students laugh when I teach. Its the most annoying thing I ever felt in my academic life so far. I always think, why some laugh while others appreciate my way of teaching? Its very puzzling. At the end of my first trimester I received a very positive feedback from the majority students. But just those couple of giggling students ruin my whole confidence.

Is it the way I speak? I look average too but why why that happens with me?

Is it normal in academia? Did this happen to anyone else? And how I can deal with them?