The flexible mounts for vibe pumps I've seen on home machines where not tightened well enough to the machine body with the result they really did not work. Once firmly tightened the noise was reduced a lot (use big washers).

HB wrote: I was surprised how far the vibration would propagate along the water line. It literally would cause buzzing in the mounts 20 feet downstream from the pump. I blame most of this on the pipe material

Remember that water is a superior conductor of sound, and is not compressible, so that any pressure in the pipe twenty feet away is the same pressure in the machine. Same reason your car stops when you push on the pedal.

Sound is simply vibrations of air molecules, compressions and rarefactions. Look for things that will move a lot of air (side panels, top panels, etc.) and find ways to isolate them from the pump, as opposed to isolating the pump form them. It's just another way to look at the problem. Start with the moving air, and work your way back to the source. Truth be told, if you have a pump in free air, it makes very little noise. Quite a bit of the noise heard in the bedroom of sleeping mates is transferred through the counter, and the framing of the house. Low frequencies like 60 Hz tend to be difficult to stop, whereas shorter wavelengths tend to get dissipated over distances more easily.
Another tack to take with pump mounting is weight. If add a fairly large weight to the base of the pump, and them spring it, it makes the actual moving parts to static parts weight ratio large enough that the working parts aren't as able to make the chassis move, thereby reducing vibrations and reducing noise. Mass is usually your friend in dealing with low frequencies.

Oh, and you can do the mods or the manufacturer can do the mods. It's only money.
The reason that most of them make a lot of noise is that the coffee is the same, loud or quiet, but the machine is far more expensive quiet and most people don't listen to it when they buy, they look at the price tag.

Interesting discussion. If you isolate the pump from the machine the machine is isolated from the pump Anything restricting air flow around the pump is a bad idea. Anyone got a spare coil for an Ulka?

The pump innerds work against the coil which can be isolated from the rest of the machine. That is what the rubber mounts are for. Mounting the rubber mounts to a hunk of material like a 1/4 inch thick by 2 inch wide piece of stainless steel and then mounting this on rubber mounts to the machine would help. Also make sure the plumbing lines leading to and from the pump are flexible and have a curve in them.

As pointed out some vibration can be coming from the water in the plumbing which also will be damped out with the flexible lines. These pressure pulses will get worse as it comes to pressure.

I never thought the noise was that bad. The proper isolation of the pump shouldn't be much of a price difference and sounds like it could be a big selling point. You could always turn up the radio.

Lorrin