This is the 12715th most frequent Russian word.
котла
"Котла" is the genitive singular or accusative plural form of "котёл," meaning "boiler" or "cauldron."
The word "котла" in this sentence specifies a boiler, using the genitive case to associate 'sound' with 'boiler'.
Звук котла был слышен в пустой комнате.
The sound of the boiler was heard in the empty room.
In this sentence, "котла" refers to a boiler, specifically using its genitive case form.
Мы посмотрели на старый котла и решили его починить.
We looked at the old boiler and decided to fix it.
Here, "котла" denotes a cauldron or pot, again in genitive case to indicate possession.