I had a U2 for about a year and a half, and the motor packed in the other day so I had to go buy a new one, that one was silent and I thought I'd get the same so as I thought it'd be the same, but it rattled, and was frustrating. So changed it like I said but this ones the same if not a bit louder. I asked the woman in the shop about the Elite Stingray as it said it was quiet and i checked on my phone and reviews said it was quiet, but she said thet weren't as good as the fluval, so I got the same one again hoping it turned out the other one was faulty. I've no room for an external one unfortunately.
It's fully submerged, without the venturi on, I've turned it upside down and got the air bubbles out, and I've pulled out and cleaned the propeller. the insides all as it should be too, I've no idea what to do next