The cold weather is here and yet again I have the same problem: humming radiators.
I have done a lot of web searching and forum reading and not found any solution.
The system is an oil burning furnace which heats a two-story house with a single zone by hot water. There is a circulator pump. Sometimes when the system is running a medium-pitched hum occurs which seems to be coming from several of the upstairs radiators, but it is hard to tell because it is a very ethereal hum.
It has nothing to do with air in the radiators. I have bled them and it makes no difference.
One thing is that the hum is much more noticeable since some work was done on the radiator a couple of years ago. I think all they did was replace the oil pump (not the circulator).
How can I figure what is causing the hum and fix it.