Powerhead Clicking Sound

[Musicims]

So weird way to know it's time to clean my powerheads I can hear a faint clicking/popping/snapping sound coming from the tank. After they are clean the noise goes away until they get dirty again. Attached video link of the sound. Beware of the loud click in the middle of me switching the pump off then on again, but you can hear a considerable amount of the clicking right after they are turned back on. I can also get it to happen if they are getting dirty but not making the noise yet if I simply turn up the speed. Tunze 6105's here.

https://photos.app.goo.gl/QgwrstmBAz1UzNvQ8

 

[vetteguy53081]

Its foreign material such as shells, algae and other matter in impeller and starting to touch the blades