You can place styrofoam or cork underneath it to dampen the vibration. You could also use a mouse pad(s), but the other two materials would probablly be cheaper.
See if you can find the cause of the vibration....open the unit up and make sure there is no air in the impeller. If there is, and you release that, it should run quietly and without vibration. But, if you can't find the cause...do what the Captain suggests and that should take care of it.
that last one is probably a better idea. I wouldn't put styrofoam or cork in my tank, but that's just me. Unfortunately, Mags aren't known as silent pumps, but suction cups help.
mine on my FW vibe like crazy i have a 12 and a 16.. but i have pilter stuffing under it just to cushion it.. but the suction cup idea seems alot better, i just had to do a quick fix for new abt a yr ago... lol
I only suggest trying to see why there's vibration because I've used Mags extensively in both submerged and dry applications and they are absolutely silent. So, I always suspect that if they make noise in someone's case, there's a reason for that and it can be remedied.
sometimes it means theyre on their way out.. ive had a few go bad bc in the FW theyre not submersed.. in the SW theyre in the sump and never have problems(usually)