So I bought a brand new fluval 206 canister filter for my 20 gallon and meticulously (or so I thought) followed all the instructions for setup. I am finally at the step to prime it to fill it with water and I give it a few pumps and nothing happens, a few more, still nothing. I then vigorously pump it over and over and no water is moving at all. I spend the next 30 mins looking up what to do to get it to prime and nothing is working. Finally in desperation I take it apart and look inside and there I see a small piece of foam holding open the intake flap (facepalm). I remove the foam and it primes perfectly with just one pump. I plug it in and it quietly hums as it seems to be flawlessly filtering my tank. Until a few hours latter when I hear this horrible rattling noise and bubbles spurting out. I panicked and unplugged it immediately. I then spend the next 6 hours reading forum posts and adjusting everything I can think of. I reattached every fitting re cut the hoses to be the exact length with no slack tried to shake the air out of the canister until I notice that every time I open it up the impeller door is slightly ajar. So I figure the impeller must be actually rattling around in there. I try everything to keep that door closed and nothing is working, I was jamming stuff in the tabs and even tried duct tape, but it would always just pop back open and rattle within about 20-30 mins. At this point I had given up and was about to take the whole dam thing apart to return it. Before I did that I decided to watch some guys unboxing and review of the filter on youtube just to see if other people were complaining about it too, I watch the guy open the box and start taking out the media containers. On top of the first one he takes out I see this little white lid with a raised circular rim around it that looks like it would sit right up against the impeller cover keeping it from popping open. I facepalm my self so hard that I hurt my nose. I run over to where I was originally unboxing the filter and find that part sitting hidden under my recliner. The filter now runs like a dream and I feel like an idiot .