Loud noise during boiler start-up

I am once again trying to find the solution to the 'music' from our boiler. First a brief description: We have a six year old Weil Mclain model 1088 series 1 10 section cast-iron boiler W/ a Power Flame dual burner which we run strictly on 'gas' only. There is a small tankless heater installed on the side of the boiler which is used as baseboard heat for the basement apartment. It is a two-pipe steam system for residential heating. The boiler has always made this loud noise ( from inside, toward the bottom) at start-up only and it is much louder on the colder days. After speaking with the boiler installers and the technician at Weil McLain I was advised that we probably would need to install a 'Blanket'. I have never heard of this and since it is a costly ($2500.00) repair, I am not sure what to do.After talking to a couple of these guys I am presuming that this problem may have something to do with 'thermal shock' noises and that this would be a 'Thermal Insulator' of of some sort. If anyone has had experience with this problem and could shed some additional light or confirm this is the most likely cause for the problem I would appreciate hearing some advice. Thank you.