Radiators

This may be a sign of a radiator that needs servicing. While all will hiss a bit, prolonged or excessive or loud hissing and release of steam could signal a problem. It could be as simple as needing a new escape valve (I don't know the proper name--it is the typically silver colored bell-shaped or round thing that is doing the hissing). You may need a new intake valve--the one with the knob that turns. The radiator may not longer be level due to building settling--the radiator should tilt, if at all, toward the intake valve (the one with the knob that turns). Your super should be able to take a look and maybe fix any problem, although if you live in a coop it is technically your responsibility and you may need to call in a plumber.

I kind of like the hissing sound of a radiator as long as it's not a high-pitched whistle. There's something sort of cozy about that sound. But the banging - oy vey.

A gentle hissing is okay but this makes a whitling sound and changes pitch. Thanks for the advice kylewest. I live in a condo and was told that teh building is responsible for the radiators. How much would a new escape valve be? I never heard the whistling noise in my old apartment.

they run under $10 in outer boroughs. most hardware stores have them.

I get a 6 AM wake-up every AM in my new apt-- a BANGING (like someone hitting the radiator with a pipe)
very day! "Oy vey" is so right!!! I plan to call the Super. I have yet to sleep through this alarm.