cooling system

Lately my liquid cooling system has been very noisy, I can hear it pumping the coolant, it gets louder and then quieter.

Looking at it though I can see air bubbles in the coolant lines and I notice that instead of coolant moving in one direction(in one tube back out thru another) it's going back and forth in tubes - is this how its supposed to move?

And the noise corresponds with the coolant flow - any ideas??

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