A Noise in the Furnace

One night, as I was getting in bed. I had heard what sounded like a door opening, and closing. At first I thought somebody was inside my home, but the noise was to small to be from a door. I got out of bed and checked it out. Thank goodness it was just the furnace. I got back in bed, but the noise didn't stop. I decided that I would call the Furnace Guy to come and check it out. The next day the Furnace Guy went down stairs to fix it, but never came up. When I went to check, there was no trace of him. For some reason I think something is lurking in the furnace, and it's probably after me next. I haven't gone back into the basement since.