The Lamp Room

https://www.youtube.com/watch?v=i3PDMXeQjMk
I operated the tutors coffee maker to show you how a horrible "BRRRRRRRRRRRRRRRR" noise its pump makes.
This is true for household and commercial coffee makers.
Why this is happening?

The pumps are similar to our wetvac pumps at work, their electromagnetic piston bounces off a big spring at one end of the chamber, this is what gives that loud noise!

Why the pump in coffee makers is a reciprocating pump? What about rotary vane pump, which is small as well?
These pumps are in use also in pressure washers.

Here they are in their component parts

Down to cost tbh.

I guess it might also be the case, that this type of pump is able to create a much greater pressure. Forcing water through coffee grounds requires a surprising amountt of pressure. Given how small the pump needs to be to fit into the machine, I guess someone has decided this is the best way to achieve this?

Yeah, in the wetvacs they pump it through a brass pinhole fan nozzle, it’s gives a wide spread underneath the vacuum head

Easy and cheap to achieve with half-wave-driven solenoid with one-way valve in series.

I must admit, the noise is something I quite enjoy as it means in a moment there will be coffee

Years ago, I took apart one of those commercial Karcher Wet Vacs (model Puzzi 8/1) and it had one of those solenoid pumps. The pump failed and it was full of hair! I suspect the dirty water tank had been regularly used to fill machine's clean water tank, and the dirt had gotten through the fine mesh.