I have recently setup a 150 gallon american cichlid tank which is filtered by 2 eheim 2217's. Since I first started them they have been a little noisy, a hum coming from the filters can be heard across the room. Both canisters are making the same amount of noise. My primary concern is that I have not primed them correctly. I followed the instructions and set them up and then I suck on the outlet pipe and waited a few minutes for the canisters to fill up. I then switched them on. I assumed that the noise would pass, however six weeks later it has not. I am sure there is still air in the canister because when I shake them air is expelled from the spray bare, however no matter how much I shake it I can't make it more quiet. Any help would be greatly appreciated.