Would this pump be a bad idea.....

[Waterlogged]

If you have the gel, get the D5. From the info provided by the user, I have reason to believe that the gel killed his DDC 3.2 by melting and oozing up into the PCB and shorting it out.

I have 2 DDC 2 pumps and when the rigs they are in are running, I can't hear them over the HDD's (I'm currently working on quieting these down now as well) and fans (when I turn them up). I suspect the D5 to be nearly as quiet.
Most of my rigs (when they are running) are within ~2-2½ Ft of my head as they are on wire shelving I bolted to the top of my computer workstation desk (88"w x 66" deep x 53" tall [including hutch], U shaped )

[super dank]

I suspect the D5 to be nearly as quiet.

The D5 doesn't make any noise at all. None.

If you touch it you can feel it vibrate, but it is below an audible frequency. Up to you if it's worth the money though. I have two D5's in my system.