Solving noise problem for Eheim 2028

[AnA]

I was having some rattling noise problem with my 5 years old Eheim's 2028 until I change the impeller.

Some pictures of my old impeller...






After I have just replaced wth a new impeller. It is not as noisy now. But it still has slight cracking noise; but this time it came from the "flow rate" indicator area. By the way, I just change to the new "spring type" (7444410-Floater, spring and holder) of flow rate indicator. The original one is "ball type" and it melted. The noise seem to come from this indicator. Previously no such noise problem. Any advise?

[AnA]

The noise is gone.....I think it could be air trap in the flow indicator. Great...