Strath

Probably the electrolytic capacitor. They fail frequently.

No. If the brake line is not disconnected, no bleeding is needed.

Has anyone shown this to Randall Munroe? How does this affect the calculations here?

It doesn’t effect the operation of the pump and takes a three second poke and twist. With no legitimate use of the speaker it would be months before it is noticed. Think they would scrub through tens of thousands of interactions with the pump and find that one person who leaned in a bit? Doubtful, and if so, minor vandalism charge and a small fine for months of quiet peace. Worth it in my book.

For the pumps that the mute button doesn’t work: carry a small screwdriver, 1/8", flat blade, insert into center of speaker then pull sideways to severe the coil wire.

Be certain your tap water isn’t softened. Softened water contain an elevated amount of salt that is harmful to plants.