I have a 105K BTU Raypak radiator boiler, similar to this one but a slightly older model (I guess mine is about 15 years old). The boiler heats and pumps hot water to 8 radiators throughout the house.
I have a suspicion it might be caused by vent pipe reverberations but I am not sure. It vents using 6" Type B (double wall) vent pipes. The pipe rises up about 5' from the boiler, then travels about 12' at a low gradient (almost horizontal), then goes up the flume from the 1st floor, through the second, to the chimney on the roof. I was suspecting maybe the horizontal part of the vent could be causing too much strain for the exhaust coming out.
Yet another possibility is that the pump makes the noise.
The boiler does work fine. It's been making this noise for about four years, which is when I moved it from the basement to the first floor.
I am looking for advice how to analyze, with reasonable certainty, the source of the buzzing noise.