How can you stop an apartment radiator from banging?

Not a plumber but it sounds like you may have air trapped in your pipes. Try bleeding the radiators and see if that helps. Otherwise it really is a job for the landlord to sort out.

I agree with @sakura. My radiators sometimes make a ticking noise and bubbling sound. It’s air in the lines. It’s easy to fix.

Slip a little saltpeter in its coffee.

Drill some small holes in it to loosen the pressure

Depending on the age of the radiator, there might be a pressure valve or release on the opposite end of the radiatior from the incoming valve, the other where you regulate how much steam you want or don’t want in the radiator. A lot of times in older buildings these are painted over with several layers of paint and you might have to get some decent paint remover, If so, do it with every window open and wear a respirator mask.

“SAKURA” is right, it is air in the pipes. If you live in a multi-unit building then other tenants should be having the same experience. I lived in a 6 story building with 90 apartments during the 80’s and we experienced the same problem in one line of apartments and the solution was to drain the entire system on one side of the building and repressurize. That had to be done in the summer, otherwise people would go without heat for more than a day and it pissed off some tenants who had to live with the noise for several months.

The only other suggestion is that the filters coming off your furnance or whatever heats the water into steam, might be in need of replacement or cleaning. That is a time consuming but inexpensive undertaking.

SRM

Bleeding the radiator is likely to work. If you don’t have a radiator key (many landlords don’t give them to the tenants), you can pick one up at a hardware store – it’ll probably cost about a dollar, and it should solve all your problems!