I bought 3 at the BRS frag swap and find them very noisy as well, I can not run them on pulse mode which is my preferred mode and be able to enjoy the tank. I run them on reef crest mode at about 80% and I would say they are about as loud as the jebao's I was running.
I did contact reefbreeders and they sent me new bushings and impeller assembly but really no different. I was almost wondering if it's the thickness of the glass, I have these on the back wall of a redsea reefer 450 and that is some thick glass, the magnet has so far held them in place but not very strongly and thinking this could contribute to the noise. Do you have thick glass as well?
I am still running them because they move a lot of water, the flow is very dispersed and the three linked up in Slave master mode with no issues. I also like the feed options of either 10 or 20 minutes depending on which feed button you press and they have a reverse mode that is great for cleaning the gunk off the guards as well as stirring up the stuff on the sand bed right below the pumps.