I have got the Koralia's as well 1-4 and all are quiet....

I havn't had to much luck with the Koralias. Had one that would chatter quite loud. Had to turn it off every night just to sleep.

I have a pair of 6080 Tunze on my tank plus the Tunze Wavebox and I LOVE them...very very quiet and in the end worth every single penny. They really are fantastic and I've never regretted the purchase. BIG thumbs up for Tunze for me!

I've got a Tunze and a Koralia running in the tank right now, and I can't hear either of them.

2 korillia 4's in my tank, cant hear them at all, and alot cheaper than the Tunzes

My koralia has been super silent.

Koralias for sure i have 3 different ones. 4, 3, 1, and they are great

My Koralia's are also very quiet.. Don't forget the orginal Koralia are not officially controllable, mine do chatter a bit at startup if being used on a wavemaker.
The new line of Koralias is controllable but they are more money than the originals

i have found my vortech to be very quiet as well i just need to find a quiet skimmer pump and stop the gurgling toilet noise my overflows make