I have a relatively new oil furnace, probably about 10 years old. The burner unit is a Beckett. Four years ago, I had the tank and lines replaced. As of late, I've noticed a banging noise, similar to someone beating on a metal drum. It seems to be related to the blower fan. I was listening to it in bed the other night: The thermostats trips on, the burner ignites, the fan runs for a few seconds, then "BANG." The fan shuts off. The fan tries again and "BANG," shuts down. This goes on for several times in a row. I went down into the basement, removed the cover to the fan assembly and turned the heater on to watch it with my own two eyes. No noise. The fan runs just fine (at least while I'm watching it ). Anyone have any idea what gives?