NT

Seriously, no help?
c'mon guys, some of you out there really know your stuff!!!

As long as it's a closed system I wouldn't worry too much. Use Core Temp or some other utility to monitor temps. Fluid dynamics change with temperature so try to correlate whether you hearing this during high CPU usage or actually just randomly. Turbulence or roil within pipes can create sound and is my guess. It's possible even without air pockets/bulbbles.

Fluid dynamics is a science all of its own.....chances are it's a combination of localized heat and route/layout of the piping.

Okay, i'll keep coretemp up on the desktop and monitor it for a day or so and see if i can track any patterns, thanks.

Jafo, if it was the layout of the piping, would the issue not have presented itself from the start? This has only been the last few days, and for about the previous month all was fine, though i certainly don't claim that's not the issue.

So - I'm a huge computer nerd.  I must have built at least 100+ computers for myself and others (that estimate is probably a little low, believe it or not).  I've toyed around with overclocking for myself, but have found the gains minimal - eg I don't care if I'm now 10k more points on 3d mark.  I care if everything I do runs perfectly and fast.  That said, I've never bothered with watercooling, only on air.  And even then, I don't see a need.  I see no slowdown in any game on any settings with my current rig and I'm only using an air cooled I7 950 at 3.07.  I did overclock it... can't remember how fast I bothered to take it.  I want to say I topped 4ghz on air (I use a coolermaster badass fan (eg gigantic and very capable)).  Anyway, running that and finding it stable, I only ever noticed improvements in benchmarks - not actual in game performance (does 1million frames a sec make a diff to you or is 60 fps fine).

So, I'm wondering - are you just in the enthusiast sort of mindset and want to come up with the fasting thing possible or are you actually seeing real world benefit for your ocing?  For me, I'm not seeing a real world benefit and have just reverted to factory as I'm probably not going to upgrade for another 6 months (side note - pacov upgrades every 6 months to a year - he loves trying new tech and loves tom's hardware guide - give that a look if you don't know about it - its much more commercial than it was in the past, but still provides excellent benchmarks and reviews on the latest stuff.

Hey Pacov!

Actually, the level of ocing i am doing and have been doing is and was quite achievable on air. I was using on my old rig the Thermaltake DuoOrb cooler, and had planned on migrating that to this new rig. (I won't get into the hassle i had finding a bracket that would work with both the lga 775 cooler and my new lga 1155 board, but i did) But the ram i bought, the heatsinks are too high (Corsair Vengeance with 75mm heatsinks) and the cooler wouldn't fit.

After trying a few other coolers, i then had to consider water. so it was a necessary step just to have reasonable cooling and still use all 4 ram slots (4X4GB). I had considered water before, just because i can, but found the DuoOrb to be a fantastic cooler and on my old, but still trusty Q6600 i managed to post on 4.0GHz (2.4GHz factory) in my Antec 900 case.

Im in the same case now with new build and have had the i5 to 4.4 just to see if i could, but dropped it back to factory, and have been running that way the past month.

Anyway, i haven't really answered your question. I mess around with ocing for fun, but have zero need to do it, nor do i need the water cooling other than it was the only suitable cooling solution, form wise. I haven't built so many rigs myself, perhaps 10 to 15, but this is the first time i have ever messed with water. It's a great talking point, none of my friends are too computer literate (hardware wise at least) and had never seen anything like it, but if i could have used my DuoOrb, i would have!

I used to love Toms, but since the site redesign i haven't been as much a fan. I don't really care for the new look or the new presentation of the charts and such, but it's still an invaluable resource when looking to update ones rig.

Since the earlier post i have been running prime95 and been checking the temps when in sync with noise occurrences and i can't say i see any pattern, temps are stable, both under load and at idle.
I'll keep scouring the interwebs and i hope more help will surface here too!

Okay, seems i have pinpointed the cause of the noise, but the why or how eludes me. The reservoir was down to about 2/3rds, i was letting it drop at it's natural rate so i could test and be sure the built in low level warning was going to work. Having not to keep an eye on the res level was going to be a plus.

I was trying to think how i could better explain the noise and i thought a mini waterfall enclosed in a box might describe it better, which got me looking at the res. I don't know where the inlet and outlet feeds are in the res, and i can't imagine it being at 2/3rds would leave either one open, but i refilled the res to the top mark and the noise has ceased.

Can anyone explain how this might be happening?
Much appreciated.

Well since you say it sounds like a quiet waterfall...  you don't think the return flow to the reservoir was making the noise, do you? 

Well, yes and no.
Let me explain...logically, yes it made sense, but the return pipe is lower in the res then the level the coolant was at. It's an odd setup.
The coolant level in the res was clearly above the intake pipe, and well above the out pipe, so the noise made no sense. The only thing i have been able to summize, is that the level was sufficiently low that a current, or disturbance in the flow, was being created, but i would have thought that would result in a constant noise, not one that comes and goes.

I'm hardly an expert in fluid dynamics, but the noise has ceased and the res is at the high coolant mark. Unless the res is multi-chambered, and it looks like that it could be, though i cannot fathom why, i can't explain why it would make any noise whatsoever, at least at the levels i had....

Hi.

In your water loop ...

Do you have any sharp bends or is your piping nice and smooth or do you have tubing flattened out somewhere. Water rushing trough narrower gaps than in rest of the system could produce that noise. The only thing is noise would probably be constant. 

You might find answers you are looking at on this forum

http://forum.watercoolinguk.co.uk/

they helped me a lot when I was building my first water loop.

@Pacov

I have corsair H70 water cooling kit on my CPU which is factory closed system.

I managed to get my i7 920 which runs 2.66Ghz at stock to 4Ghz with temperatures on idle at 40C heavy use 55C and under prime95 70C. H80 is very easy to install compared to custom loop.

Benefits: Well I can play late sins game without game turning into slide show. PC boots up faster all programs run faster. Basically It is like I have new faster processor inside. Mostly I see differences at programs that don't use multi threading since there is not many programs I use that pushed all 4 cores with hyper threading to their maximum load even when I was on stock settings.

I added some pics of my system just for....

You can localize the source of the noise very prcisely with an engine/mechanic's stethoscope. Maybe if you have an auto mechanic friend, he'd lend you one or a neonatal stethoscope (if you have a nurse friend working in that area).

I figure the water arrives higher than it leaves. When only 2/3 full, the water made noise 'falling' to the fluid level and mixing there. I could be wrong, but that sounds like the reason in light of the noise disappearing after filling the tank.

@Greg, thanks for link, i'll spend some time lurking on those forums for sure!
As for pipe layout, no it's very smooth with no kinks or bends.

Doc, thats a great idea! I can get my hands on a mechanics stethoscope! i'll try and replicate the noise again and then see if i can pinpoint the exact source.

The intake pipe is higher than the outtake, but it feeds into the rad, which is situated lower than low coolant mark on the res. What i cannot see is how, if at all, the rad feeds back into the res. I'm not sure if the rad feeds back to the pump or the res then pump. I'll get some pics up to show my meaning.

Just remembered

If system is not properly bleed you will get noise when air bubbles  are moving around throughout system. It is a sound like water is running