My return pump is a Mag 7. I bought a 100% silicon trivet pad from Target and put that underneath it to dampen the vibrations - that made a decent improvement, but it still makes a buzzing noise somewhat like a cheap fluorescent light.
To contrast it, my skimmer has a much larger pump on it (a Bubble Blaster 5000) and it's a very soft, low frequency hum. It's obvious when the return pump is on, but you have to listen carefully to tell if the skimmer is running.
Anyway, my Mag is at the top of my hit list for equipment upgrades, but is tolerable for the time being. Definitely nothing like a freight train...