Did you think about asking them why they were laughing? I can see maybe being to anxious not to ask. Giving preentations in a formal setting is can be a bit trying. Especially if it is in front of people you do not know very well. Something that always helped me through them was imagining everyone in their underwear or dressed as clowns. It is a tip received from someone a long time ago when I was young at one of my first leadership courses.