If any of you guys are looking for a cheap way to really cut down the noise on the DP400, here are some pics of the box I built:
https://www.dropbox.com/sh/7ddhnyfshrsd3zp/AABYpwCGv3_4vIrohqXqpmv1a?dl=0#/
It’s really easy and total cost is about $15. I went to Michael’s Craft Store (you can also find the materials at Wal-Mart but Michaels is closer to my home) and got a heavy cardboard box - the ones used for storage - about the size of a large shoe box. Get some seat padding and cut out a piece for the top and the bottom of the box. You’ll need to decrease the thickness of the padding and the layers peel apart really easily. Get a can of spray adhesive and paste the padding to the top and bottom. The box I got had a label area on one side so I cut that part out so the USB and power cord could come out. On the other side, I made a small hole just large enough for the tubing. The extra padding I place inside to help to muffle the sound more.
It’s crude and simple, but it works. I’m designing a better box now, but for the time being, this one does the trick.