I have one that is rattling on low speeds on the controller. It started to do this after a week of completely quiet functioning. I have gone from the 2 dot speed to 3 dot speed and initially it worked, now rattling again on the low speed. It appears that when the unit is in off mode while the other unit would be on it has trouble getting going. The rattle is not all of the time, intermittent for a few seconds then kicks into high gear, then back to low it rattles. I am somewhat frustrated but overall these are great for hard to reach spots adn small tanks. I have yet to take it out of the tank and re-sit the blades in the motor. I thought that might help to stop the rattle on start up in low speeds. In higher speed it is quiet as they come, but I don't want it on high speed all of the time or I would have gotten the 6045's.