FWIW I insulated the cabinet box my dishwasher sits in with EPS insulation panels (the rigid foam panels you can get at the big box store) and it does cut the noise. If you don't have room this won't work though.

I actually was thinking the same thing - do a parts breakout comparison of a low-end Bosch and whatever their quietest machine is and look for differences. I'm fairly sure it's not just insulation - at one point a few years ago, the top-of-the-line Bosch included a fancy hermetically-sealed toekick rather than just the usual piece of metal you adjust to drop down to the floor. There's also how well the motors and pumps are insulated from the rest of the machine, and such.

This page off their US website highlights their quietness-related technolgies (click on "Learn More" under 'the anatomy of quiet'). They also show the exterior insulation:

Mine doesn't have the cotton blanket shown in the picture; only the higher-end models have it, and that's what I'd like to add. (but not by buying it as a spare part from Bosch which would likely cost 1/3 the price of the whole dishwasher).

I think the motor and pumps are similar to the European ones. But the fancy adjustable third rack hasn't made it to the US yet, nor has any 18"/45cm dishwasher with a tall tub or a third rack. (Or those amazing washing machines that hold a 9kg load despite being only 60cm wide and deep - how do they do that?). Also, we don't get their latest improved-design racks seen in these videos:

VarioDrawer Plus upper/middle rack

New Lower Rack (German)

The advanced cutlery rack is available under the Thermador brand. As is StarSpeed - a 20 minute wash cycle that stores hot water in a tank next to the wash tub so one can run one 20-minute wash after the other. But you will need to let the DW pre-heat for 30 minutes... Zeolite drying has not yet made it to the US, unfortunately.

Those 8 kilo washers just run three hour cycles to get the items in the over-stuffed drum clean. It's like stuffing 40 lbs. into a Duet: let is soak and rotate for a couple of hours and it'll come clean eventually.

Wow - news to me! Ever since Thermador was bought by Bosch/Siemens, Thermador dishwashers have been near-clones of Bosch machines until now. Whirlpool at least uses different racks and various trivial differences like difference wash arms, but Thermador (and even Gaggenau) generally changed nothing but the control panel, and then only slightly. (Before the BSH buyout, Thermador dishwashers were clones of Waste King dishwashers, the sink disposer folks).

Now they have a few unique features to separate them from Bosch. Time-remaining displays are commonplace, but Thermador's projects it onto the floor!

Also, whereas Bosch dishwashers (at least in the US) don't have illuminated interiors, Thermador does - and in blue to match their other appliances. Not sure if blue lighting is as useful as white, but it does look cool:

It also has the new rack designs for the top and bottom racks (and maybe the center - not obvious from their pictures). I really like being able to store glasses on the bottom rack and larger items on the top, which makes it easier to load and lift heavier items into and out of the dishwasher.

But I see they still claim only 44db sound level on their priciest dishwashers, whereas Bosch claims 39db. Wonder what is different or missing in the Thermadors.

If by fancy adjustable third rack you mean a cutlery rack ala Miele, they are available in Bosch DWs now.
I'm sure that adding a blanket would help sound attenuation. What Bosch DW model do you have? Is it SS?

I don't have the model # handy (it's at another house) but it's the second from bottom of the line, about a year or two old. One of the Ascentia series where the frame and bottom of the tub is grey plastic but the rest is stainless steel.

Some US Bosch dishwashers have an upper third rack now, but not the adjustable type shown above where you can push down the outer portion of the rack on the left and/or right side to make room for cups, short glasses, or larger items like soup ladles. Elsewhere in the world some Bosch machines have these new racks, but in the US it's thus far restricted to the two top Thermador DWs (and maybe Gaggenau, haven't checked), perhaps because here Bosch is BSH's least expensive brand, generally below Thermador pricewise.

As for sound insulation, I wonder how much of the noise seeps through the countertop and side cabinets (which is what the insulation blanket would help) rather than through the front door, toekick area, and just general vibration from the motor, pumps, and moving parts resonating through the floor and other fixed surfaces, which added insulation wouldn't help unless I open up the machine to install it.

Part of the reason Bosch dishwashers are so quiet is that they separate the pump and drain motors and mount both on a large plastic base via vibration-absorbing fasteners that don't transmit much noise to the outside.

This is an interesting idea. I'm curious how well it will work. Good luck with this.

Don't know about Bosch, but my KA DW (a KUDE70; ~40db) was clearly much quieter after its (insulated) toe kick was installed. That was left off a few days to make sure there were no leaks. I'm happy with how quiet it is; not sure there would be much point in having it any quieter, though.

It may help to think of this problem as like a sieve: vibrations escape anyway / everywhere they can. So plugging a few holes makes little difference until you block enough escape routes to significantly reduce the volume of sound vibrations. Kind of like heat loss in an old house: there are so many little places for heat to escape that fixing a few spots, even the biggest ones, doesn't always make as much difference as you hoped. Its why old houses don't need make-up air as much as new ones.

This implies that a lot of little things reduce the sound levels across models. Adding insulation seems the easiest and cheapest approach to reduce noise, as long as there are no gaps between insulation sheets allowing sound to escape. Comparing schematics across different models should sort out if only the highest cost models add the more expensive fixes, such as quieter pumps, etc.

yeah I'm planning to compare schematics between low- and high-end models when I get time - I'll post the results here.

And yes, I've found how you install a dishwasher can significantly affect sound level. Sloppy installations that leave gaps around the sides, top, or bottom increase noise. I've found putting thick stick-on felt pads, the kind sold for use on table and chair legs to protect floors, can reduce dishwasher noise when applied to the four legs, which is easy since they just stick on after you peel off the backing.

Most noise escapes through the open area between the kitchen's toe kick and the dishwasher door. We have a BOL dishwasher with custom panel, currently, that's 55 dB. If I stuff a blanket between toe kick and DW door, it becomes much quieter. If I hang the same blanket in front of the dishwasher, there's not much change. So, in my case, most sound comes from underneath/the bottom of the appliance. If you look at installation manuals from Bosch, you can see that they include adding insulation strips around the bottom of the units and there's even a rubber skirt that attaches to the custom panel in order to shield more sound off.

So I'd say try insulating the bottom (pump etc.) for most dampening.

Alex

BTW: Bosch is presenting dishwashers with color screens and an option for 66% faster cycles at the German IFA (like American CES) at the end of august.

Here is a link that might be useful: Bosch dishwasher

yeah I've found that to be the case too (hence the hermetically-sealed toekick area on the high-end Bosch I mentioned upthread). On an old Maytag dishwasher I had at a previous residence, alot of noise escaped just under the countertop, above the control panel - putting a folded towel there quieted things down considerably. But I don't notice much difference doing this on Bosch installations I've done.

"The super efficient water management of the Bosch ActiveWater Eco dishwasher reuses the clean water from the final rinse cycle for the first wash of the next load. This provides for the incredibly low 7-liter water consumption for 13 place settings."

This sounds like a good idea at first, but wouldn't the rinse aid (Jet-Dry, etc.) mixed in with the final rinse hurt washing performance, counteracting the action of the detergent? It would be like mixing liquid fabric softener in with washing machine detergent, or creme-rinse conditioner on your hair along with shampoo.

The rinse water is used for the pre-wash. not the actual main was. I see the article is a little unclear about this. Plus, rinse aid is mostly surfactants - just like detergent - so it won't harm washing performance.

FWIW, Miele claims their dishwashers use slightly more water than "certain other ones" but this is only because they don't reuse water, which is "unsanitary". Might be some truth to it but Bosch is also Miele's biggest competitor in the high-end sector so I can see where this claim is coming from...

My Miele Diamante Plus was installed two years ago and is pretty quite. One thing I noticed is that the unit has a metal enclosure on the top and all sides, with the sound insulation between it and the stainless tub. I think this is a good design, as my previous GE and Electrolux units had just the exposed insulation. There is couple inch gap between the tile floor and the bottom of the Miele, so I stuffed in a large cotton body towel to help absorb any sounds that may be coming from that area, plus the toe kick is 1" wood.

The most sound I hear is the water being sprayed when the unit isn't very full on the bottom rack. But with a full load, there is less noticeable water sound.