The best way to fix this is to get rid of them. They are great utility pumps, but only if you don't mind noise and I wouldn't consider them a full-duty pump. I use them for water changes and the such. Granted, I have one running a media reactor, but... only until I get my new manifold plumbed.
If you are using this for flow inside your tank, I have a couple of koralia's in a box that I'd gladly trade for a mag 1200 or even just give to you. Would that solve your problem?