Last night I found a perfect cardboard box in my recycle pile for testing the motor again. This time I placed the motor on four ~3/4” thick sorbothane mounts, then place 2” denim insulation along the sides and top. I cut a hole in the cardboard for the driveshaft to emerge from, but did not place insulation on either end. Noise was still evident, but the meter dropped back down into the low 40s. I’m thinking a more robust enclosure (made of wood) and perhaps a more appropriate sound insulator (something designed for whatever pitch it makes) on all six sides would bring this further down. Applying some mass loaded vinyl to key portions of the motor may also help.
Of particular note - the sorbothane mounts helped a bunch in reducing the annoying pitch. I found the sound to be much more tolerable. However, they are very, very soft. I’ll need to be sure no radial force is on the motor as well - it is rated at several dozen pounds, but even a little radial pressure makes it notably more noisy.
