Hissing And Knocking Radiators

Carol: ...Heat is coming up & making a lot of noise.

Heh. Down here in young Oklahoma, all I've ever known was modern gas forced-air central heat (steadily droning at the moment), but that decade and a half we spent in our 100-year-old Chicago apartment building, we had the boiler and steam radiators. Hissing and sometimes knocking were actually comforting sounds on those freezing Windy City winter nights.