No need to send the old one back. The clicking noise is caused by one of two things, the slack of the prop or the magnet being pulled down and clapping on the bottom of the pump. You should have also got a small black disk that is to be used to replace the stainless steel one. It is thicker and will solve the downward pull problem if you have that problem. The disk is very small and usually we tape them to a paper or the card tag of the drive unit.