Clanking steam pipes are a symptom of water being slammed against elbows and fittings by the high speed of the steam picking up water and slamming it against the pipe. Also, when hot steam passes over the condensed steam that is still close to the boiling point some of the steam ‘explodes” into vapro again making sizzling and clanking noises.
Over many years, buildings settle, so pipe runs that used to slope toward the boiler move downward to trap water and steam in pockets, making them available for steam to pick it up and splash it at high speed. Water moves around obstacles gently at low speed, but at high speed it is like steel shot and can actually break fittings off the ends of pipe when stopped at high speed.
To make the problem worse, steam moves faster the higher the pressure behind it, so making the pressure in the boiler higher than necessary makes the problem worse. A problem is that people know less about steam as the generations die off. Superintendents sometimes think that if the steam pressure is one pound, the heat is better at 5 pounds. However 1 pound of steam pressure in hot pipes will rise to the top of the World Trade Center, so 5 pounds will heat the superintendent’s astronaut relative in space. After all, clouds are cool steam in the sky.
So see if the pipes can be levelled and the pressure reduced to where it is supposed to be and the world will seem a quieter place in spite of New York sirens and traffic.