I just bought two of these. The noise surprised me, one louder than the other, but even the quieter one is not acceptable. I've used Maxijet 1200s and Hydor Korallia powerheads previously - never heard more than a faint hum from them. The Maxis just went back in my tank. What to do about the noise from the Nanostreams - is it supposed to go away by itself or what?