Pics of the Thermaltake Bigwater. I grabbed some off the net since trying to grab some from within my rig wasn't showing the detail. My unit is identical to these.




The top hose is the intake and it feeds into the rad. Perhaps with a lower coolant level, the rad was not filled up and there might be the noise, as the coolant feeds into the rad, not the res?

I followed all guides i could find about bleeding, and i'm pretty sure i did it right, since it ran fine with no noise for the first month or so.
If it was not bleed correctly, would the noise not have been apparent from the beginning, and would that be a constant noise?

Loop should be 

Reservoir ->Pump -> Radiator -> CPU/GPU/RAM/HDD -> then back to Reservoir

And reservoir should be higher than the pump is inside the case.

Not necessary. Noise would be heard only when bubbles are moving trough the system. They could get trapped behind an obstacle or in some corner inside radiator. Until conditions are right they are trapped there and with a change in temperature or pressure of coolant they get released until they get held again...

Eventually sound should cease because one of functions of reservoir is that if filters bubbles out of the system. 

 

     

The reservoir only replenishes the circuit when the volume is sensed as low most likely, and probably sounds an alarm. Could the alarm have been the sound you described?

The noise is most definitely not a 'waterfall' as I thought. The reservoir is only connected as replenishment when the fluid is sensed 'low'. Might you have heard air being sucked into the reservoir?

To duplicate, just lower the fluid level to the 'low' point or slightly below it. BRIEFLY.

More detailed pics:

 

 

 

As you can see from the pics Greg, it's a all-in-one unit, so i hope the design is as it should be. One would assume so anyway.


To the best of my knowledge the alarm is just a light on the front of the unit, in any case the levels were well above the low mark so i'm sure no alarm would be sounding.
The level the coolant was at when the noise was occurring was about 2/3rds the way from the low mark to the high mark. Well above any point where i would have thought there would be any issue, noise or otherwise.


Yes, i suppose it could be. A poor seal perhaps on the res cap? I'll look at that.
I've rung a mate who will drop by later today with is stethoscope and i'll drop the coolant level and see what happens. If possible i'll record the noise and post it.

Update.
So, the noise was not repeatable, so i'm going to have to assume one of two things.
The noise was air being sucked into the res, and when i filled the res back up i tightened the cap sufficiently to fix it. (not that it was lose or anything.)

Or,

It has/had some air bubbles trapped, and refilling the res was enough of a change in the system to dislodge them, or it's still there and yet to raise it's head again.

In any case, i'm going to pull it out, re-bleed the system following a guide on the link Greg provided (thankyou!) and see how i go.

Appreciate the help all.

Things to consider regarding the water itself.

 

If it's tap, you're putting massive amounts of crap, including things that become a gas, into your cooling system.

 

If it's carbon filtered, the filtration process puts a lot of gases into your water, which can be worked out, and there's still a lot of crap in it.

 

R/O or distilled is the only stuff you should ever put in a cooling system, and not fresh.  Letting it settle for a day or two will significantly reduce the amount of gas in the fluid.  It's also a good idea to keep the reservoir full, particularly if the intake process results in stirring of the surface.  Water absorbs oxygen naturally.  If the reservoir is largely static, there's little need to worry about settling, but putting crap in there will most definitely change the dynamics of your flow over time as deposits build up.

It's the Thermaltake coolant that comes with the kit. I'd never put anything else in the system.