No zoning, three air handlers-- then most all the above...never mind :)
But you could still have a timer in your home for ventilation which cycle the fan(s). Or, in your thermostat you could have a ventalitaion/circulation cycle and the clunk you hear after the air handle shuts off is "tin canning" from your duct work. But that should me more then obvious to anyone in our field, I would hope.
Tin canning comes from the duct expanding and contracting when the air handler blower starts and stops which pressurizes the duct work.
My bet right now with this new information is "tin canning."
Here in our neck of the woods, we call it "oil canning":)
Whoops! You are right! ..been such a long time since I used that term.
Okay, I'm "canning" and it's not jelly :) It's 7:55 am in NY and like clockwork my noise just chimed. The ventilation explanation makes the most sense ... since this is not happening for hot water or heat. Where would this timer be for ventilation? It can't be in the themostats because when all 3 are off, it's still happening. And what would cause this just to start the past 2 months? I think you might be on the right track and I will pass it along to my repairman -- who is not an HVAC guy but strictly for the boiler, which might be my other problem. Thanks for all the info!!
Delta, okay, Yea! I think I found it. Got onto the First Co. website and checked out the product manual for what I think is my air handler. And there it is --- pump timer -- energizes pump for 30 seconds every 6 hours. So I'm assuming that this is what is calling for the boiler to turn on and the noise I'm hearing (the tin canning) is when it turns off. Now the question is what is causing the noise -- is there something wrong in the air handling system or in the zone valve in the boiler. Thanks for totally narrowing this down. And again, I now know more than I ever wanted to know about how my house works!!
We are addressing two parts of your heating system. One part is the air side which has to do with moving the heated air.
The other part is you hydronic side which moves the hot water from the boiler to the First Company hot water coil located inside the air handler.
Looks like you have found the cause for the constant 6 hour noise problem with the internal timer. That timer, which should be in all 3 air handlers, is to help keep the hot water pump from sticking from non-use. It's a good thing. But there should be no noise from it or due to it.
So, looks like you have a problem in your hot water circuit due to but not because of the cycling of the hot water pump.
I would now place myself in the area of the noise that you hear when the timer is about to come on. Then chase down the noise to as close to a spot as you can get.
Then it's time for your boiler guy to come back where you can show him what you found. He can move the timer so it will energize and then he can track down what is causeing the noise.
Let us know.