UPDATE:
So I did a mini-mod to my BRS reactor tonight. With the doser mounted straight to the drywall it was causing it to resonate through the wall and amplify the noise fairly significantly. In fact, when it was running it was the loudest piece of equipment in my setup. Here's what I used to fix it.
I hit the craft store and picked up a foam sheet. This particular product is a semi-rigid, closed cell foam called
"Foamies". It comes in various thicknesses, this particular one is 6mm. This stuff would also be perfect as an anti-vibration pad for lightweight external pumps. Best part, it costs a whopping $1 for a 9x12" sheet.
Here you can see how thick the foam sheet is. 6mm or ~1/4" in thickness.
This is the bracket from the BRS doser that typically gets fastened directly to the wall.
I traced around the bracket with a straight razor to cut a matching shape out of the foam sheet.
Finished cut.
Here is the bracket mounted on the wall with the added foam backing installed between the bracket and drywall.
Here you can see how the dosing pump stands off the wall when clipped onto the bracket. The foam acts a barrier which eliminates the transfer of vibrations through the drywall.
All done! A simple, inexpensive, effective fix I recommend for anyone planning on mounting their BRS pumps to their walls or even under cabinetry to eliminate excess noise from your dosing pumps.