Foghorn-like sound from piping near low-water cutoff

samfrommaine

Hi--

This is not hammering. It's not like any sound I've ever heard. It's a foghorn-like sound that's intermittent and quite loud (feel the vibration through the floor).



I went down to the basement and looked. It's not the boiler; it seems to be coming from the vicinity of the low water cut-off and its copper piping. The valve drains and refills as it should. 



The system is rather old (ok, really old) and I've never heard a sound like this before. 

This is the first cold night of the year, really; and the copper tubing coming off the valve is part of a rats nest of copper tubing. I did a good deal of insulation in the basement this year, and I'm wondering if there's some kind of temperature differential that's causing the copper pipe to vibrate.

Of course, what I'd really like to know is whether I need to turn off the boiler immediately. My boiler guy said no, but he's not hearing the fog horn, either.

Thanks for any help you can give!