There are many reasons why people make weird noises when they start to fall asleep. One reason is that people can sometimes snore when they're sleeping. Snoring is a noise that's made when air flow is blocked in the nose and throat. This happens because the tissues in the throat and nose vibrate as you breathe in and out.
Another reason someone might make a weird noise when they're getting to sleep is because they're snorting. Snorting is a noise that's made when you force air through your nose and mouth at the same time. This happens because the air pressure inside your lungs is higher than the pressure outside your body. When this happens, the air will escape through your nose and mouth.