I bought a Cobalt 400 and a Marineland 400 at the same time for a project. The marineland was 10x as loud and the housing leaked everywhere (I was using it external). I replaced it for another cobalt and it is quiet and doesn't leak.
That being said, If you add a ton of head pressure to either, they both vibrate. I have a cobalt 1200 on my carbon reactor, and I have to make sure the hose or pump doesn't touch the sump because it make a weird resonance.
The Marineland I got said made in Italy, which was where the originals were made. Maybe I got old stock off amazon, guess I was lucky. This is why this site is great. Everyone helping each other!!! If I need another cobalt it is...
I have to update. Fine print on box said Made in China. I thought I saw made in Italy on it, turns out that was on my old but still running original MJ, 20 plus year old pump. You are all right. New Mj not the same and loud.