Nutter

I use the Sonpar brand pumps & think they are fantastic. I have the smallest right up to the largest model & you just cant hear them running at all really. I actually have to touch mine to feel them viabrating gently. They last for ages, are very powerful for thier size & are the cheapest pumps I can get. As the others said though, positioning is everything when it comes to airpumps. They will all make lots of noise if they start to move around or have the cord against something.

gremlin

I put a mousepad under my air pump (when I have the tank set up in the winter). If one doesn't work, you can always use 2 or 3. Another thing that works well is the foam floor pads that you kneel on (garden store area). They are nice because they are usually water proofed. They are also thicker. If you have several air pumps that can sit in a central location, you could probably fit 3-4 on one pad. Or you can get the heavy duty rubbery rug that you stand on that is supposed to be good for your feet. I've seen those at Costco occasionally. Since they are a solid rubber, they could probably be cut to size for where ever you need them.

Akari_32

i have a Tetra 3i pump and i think it would be perfect if it sat strait on the rubber feet. it sits crooked because the hose weighs it down to one side and it buzzes on my shelf. i recently gave up and put a check valve on it and put in on the floor so the carpet muffled it. other than being lopsided, it works great. i also have an S-10 Stellar and an Aqua 20-60 and i love them all, tho the Aqua is my favorite because its super quite. sometimes i forget about unpluging it durring water changes >.<