Re: Noisy first heat of day
This sounds to me like you're hearing pipe expansion noise--after a long off cycle overnight, the hot water coursing thru the pipes to the attic are rubbing against wood, a hold down bracket, etc---this is characteristic of plastic pipe (PEX usually), as well as copper.
You'll have to be there on the spot in the attic using your ears when the heat comes on---it's the only way to locate the noise.
Once you've located the noise it can almost always be fixed by rearranging the hold-down bracket, etc. until the noise goes away.