[kilauea91]

You also need to make sure the tiny hole(see photo, credit to zig on ukaps) near the impeller housing is not clogged by debris or mulm.
the hole is a curved channel to the impeller housing cavity to help purge air/relieve pressure inside the impeller cavity.
You can use bendable soft metal wire or thick nylon wire(fishing line) to clear the channel free of mulm,
or use compressed can air to blast the hole clear.

 

[kilauea91]

I use this to pick out the old bushing inside the impeller chamber.
it doesn't take any effort with the right tool.
Just be REALLY careful not to scratch the inner wall.
Any scar/damage inside may cause turbulence when impeller spins and make it rattle. Do this at your own risk.
Simply mount the new bushing on the shaft and slide it back in the cup.

As PlantRich suggested, a flashlight is absolutely necessary when doing this.

Husky Precision Pick and Probe Set (4-Piece)-60004H - The Home Depot

Ok! How do you get the bushing out of the bottom portion? Mine is always stuck!

 

[kilauea91]

Did you notice any reduction in flow? If it's properly primed and running quiet at first, somehow air got in there a while later as described, you may want to check the intake hose/prefilter/adapters(quick-disconnect, L-bend near the body) making sure nothing is clogged. A clogged intake could cause cavitation and noise. I have never seen this in my 2217, but my 2213 (12/16mm hose) would do that reminding me of cleaning the intake/outflow hose.

I even replaced both the bushings and shaft. It was quiet for the first few minutes, but now its noisy again :/ not nearly as bad as before, but not as silent as when I first got it, either.