Koralia Nano...How noisey?

[Floop70]

I've got two K1's in a 25 gallon and they are super quiet.

[DanG]

I had problems with a K3 for a day or so until I found the fix. It was almost like a grinding sound, yet the pump was spinning properly. I did some research on the net and found that sometimes if you get an air bubble stuck in them, they can be noisy. A properly working Korilla pump should not be noisy.