Check first that this isn't a routine maintenance issue. Noise from circulating water could be air in the baseboard piping. You'll need to bleed and fill. Rumbling noise from a boiler could be a restriction in the chimney or flue, caused by soot (sort of like clogged arteries). Maybe time for a chimney sweep.
Insulation between floors - how affective?
My home theater System is in a room on top of a hot water baseboard heating system in the basement. So every time the boiler fires up and the pump is circulating water I can hear it. Very annoying. Also my air conditioner compressor sits on the other side of the exterior wall but not much I can do about that.
Anyone use insulation batts to stuff in the basement ceiling rafters to deaden sound. Rockwool/roxul has some sound reducing insulation batts that looks interesting.