To start with, if you didn't have the tank removed and cleaned...and can show proof, then no warranty will be had. Also...who said the pump has failed. Just because it makes a bit of a noise. I have used a fair few of these before without failure on a single one. Doesn't mean it can't happen but it's highly unlikely. The noises can quite possibly be coming from the standard mounting frame which the pump will vibrate against if it has no padding between itself and the pump. Also if they are mounted too low they can vibrate against the bottom of the tank.
Noise doesn't mean stuffed.