Water Cooling Radiator Making Noise

[Random0541]

First off, let me mention to keep in mind that this is a 5 year build.

Specs (Not that I think this matters)

i7 2600K (stock)
16GB (4x4GB) G.SKILL Ripjaws Z 1600 (stock)
MSI Z68A-G45 (B3)
EVGA GTX 570 (stock) (at the time) recently 'upgraded' to GTX 960 (stock)
Corsair H60
Cooler Master HAF 932
Hard Drives, Optical Drive, etc.

My Corsair H60 has been doing a fantastic job at keeping my cpu cool. The only grudge I had against it was the noise of the fans so I replaced the stock fans with some silent cooler master fans later. Everything was peachy. No leaks *knocks on wood* , etc.
The 'problem' started about 3 years ago. I noticed that randomly there would be a weird noise coming from my computer. Now keep in mind that after I replaced the stock fans of the cooler my case was pleasantly quiet. So hear this noise arise was a bit strange but I disregarded it because I'm not that concerned about computer noise dampening. The noise would eventually go away about 5 minutes later or so.


TL;DR
There has been a noise coming from my Corsair H60 CPU cooler for 3 years now. I'm not that concerned about it but I finally opened up the case to see what it was. I am 99% sure that it is coming from the radiator of the CPU cooler. The closest thing that I can relate noise to would be a water filter for a home aquarium.
It's not leaking by any means, just makes this noise every once in a while (couple of times a week)

I don't even know where to start to troubleshoot the system. Any suggestions?

 

[Darkseiders]

Sounds like air bubbles in the loop. Nothing you can do to get rid of that in a sealed loop. The only fix is to replace it.