Hey hey!
I've done quite a lot of research about this lately!
What I've found successful from other people is buying a small impeller from the same range as your filter. Eg I have an aquaclear filter (renounned for rattling) if you take the impeller from a 20 and put in a 30 it should decrease/stop the rattling. Aquaclear all run from the same adaptor with the same watts though so it's effective but I'm not sure with other systems.
The other option is using a lubricant on the shaft itself and then placing the impeller back on. It's suppose to make it run more smoothly.
It's suggested to use a sylicon base but I use Vaseline with no issues thus far.
Don't be surprised if this doesn't work though, most impellers have a plastic stopper on them.
So once the impeller rotates and the stopper hits the opposing stopper, the impeller will reverse the rotation and spins the stopper in the other direction.
The tapping you're hearing is this process.
Your shaft looks fine though!��
