The CTR II reservoirs have a unique approach to securing the pump, using a single large compression ring to hold it in place. There is a sweet spot for ring tightness, too tight and there will be noise from the pump's impeller. Too loose, and it can leak a bit. If you're experiencing noise from the pump, place a towel under the unit, then loosen the ring in tiny increments until the noise stops. The best way to do this is to have one hand on the PSU's power switch and one on the ring. Start the pump, listen for rattle, and shut it off if you hear some. Loosen a little bit, then repeat until quiet.