Why do this guy who sits next to me at work make wierd bodily noises?

for example, he is always snorting and blowing air out his nose like he is upset about something. he sniffs really really loudly sometimes as well. when the office is completely quiet, all i hear is him next to me exhaling thru his nose like he has some sort of proble. i don't talk to him because he hits on me all the time. i asked if he has allergies and he said no. it's been over year, what is his problem?