Cause of noisy gas house heater?

I bought a house that was built in 1958 and has a gas furnace that appears to be about three years old (I say 3 yrs because bought house as foreclosure so no one knows exactly--but it looks fairly new everyone says). I tested it and it sounds fine and the inspector before I bought it said it is fine. But the person renting the house from me claims the heater is so loud they cannot sleep. I am trying to figure out what I can do to make the heater quieter short of replacing it, since it is so new. The guy who remodeled the house for me says he also thinks the heater is good and he likes the set up as the heater is centrally located and he says the ducts are unusually large, allowing for quick heat distribution. But I am wondering if you could suggest anything we can do/look at to make the heater/distribution of air quieter? thanks.