Zar's Sound Muffler
This mod is useful for getting rid of just those few, annoying or tinnitus-inducing sounds (like that humming sound of the substation!), without having to silence an entire category of sounds. I have refined it to a state where I feel it is worth sharing on the Portal, not least because of its configurability. It is similar to Eradicator's Safety Ear Muffs, which I used to rely on before Factorio 2.0, but it is built from the ground up to be more reliable and allow for finer control. Entities can be muffled individually by name or as a group by type; the sound volume will be adjusted by the same configurable factor.
It is made to work for static entities, but it may also work for moving entities (it will for example get rid of the bleep-bloop sounds of the Spidertron, without affecting the sound of the legs moving). I may expand the mod's functionality at some point so it also works on new sound categories used by various entities in Space Age, if it seems important.
How to use: In Startup Settings, write the type or name ID of the entity you want to muffle the sound of, optionally with a prefix modifier ("a" or "i" along with a colon) to indicate that only sounds categorized by this mod as "active" or "idle" should be affected. (It seems that only the Accumulator along with entities from some mods use the "idle_sound" property, so usually no distinction is needed.) You may want to create a backup-document with your inputs, if they are long.