Why does one of my steam radiators only come on on high and bang loudly

I have a one pipe steam system

This one heater in my sister’s bedroom only turns on when the heat is on high but it bangs LOUDLY enough for the whole house to hear and doesn’t get hot at all.
Winter 2020, It was cold, the heat was on 77 (according to them) My sister’s bedroom heater was banging loudly like usual but then the hissing always sounded like it had blowing air then sucking air like in out in out but then the gorton air vent fell off out of nowhere, no steam was coming out, as of what i saw, But the hissing noise was really loud. I told them I thought the heater was exploded. They replaced the air vent to a maid o mist 6 but it was still doing the same banging loudly and hissing weird. I always hear a gurgling sound downstairs right below the heater. This heater only comes on on high, But the rest are completely fine, the downstairs hallway Bangs like my sisters heater RARLEY but doesn’t anymore for some reason. Its bangs really loud up till this day come someone find out what’s wrong