Follow up to original post. The repair tech examining the d/w and said he found a loose screw near the fan. He did not know if it accounted for the noise. He would've replaced the fan but didn't have the part. If the noise comes back we were instructed to make another call whereupon the tech would replace the fan. (There is only one fan.) There are no other ideas as after the cycle is complete, which is when the noise starts, is when we have heard the noise. The tech said that this is the only moving part after the cycle is complete and the door has opened, therefore it is the only candidate to be causing the noise. The noise hadn't come on over the past week, so hopefully it was just part of the breaking in period and will not return.

Before we bought our top of the line Bosch dishwasher, we asked around and were advised by people who had one that they were very pleased with it's being really quiet. We too are very pleased. Now I can listen to the radio, talk on the phone, read, do whatever I want in the kitchen when the diswaher is on. The only time the dishwsher pipes up, and just a little bit, is when it's draining. And it does a terrific job washing. If you take just a minute to wipe larger food particles off your dishes with a paper towel, it works just fine, and I haven't had to clean out the drain thing yet.

Given that it is currently bothering you enough that it's a problem, I suspect it won't be possible to make that particular dishwasher quiet enough to not disturb the peace of your home. A new dishwasher is probably in order. (I really hate it when I buy something and it turns out to really not be what I wanted!)

If you think its water hammer, install a WH arrester on your dishwasher line. They're under $15 at the box stores.