Thanks for all the support here because there's some confusion on my part.
I have a forced hot water system; not steam, as I previously noted. The system that controls the heat is in the basement and I have radiators on the first, second, and third floors of the home. The radiators on the first two floors work fine. There are three rads on the third floor - one is hot to the touch, one is warm, and the third is cold. When I try to bleed the rads on the third floor, sometimes water and air come out, sometimes just air, sometimes nothing happens.
As far as I can tell we don't have hard water and I haven't heard any other noises coming from any other place other than the radiators. I say, as far as I can tell because we've only lived here for a little over a year so I don't have much experience (hence the confusion before) with the system.