Weird resonance from heatercore...
 

I have assembled my new watercooling system to do some leaktesting. I have built the system in a separate enclosure, so for now, I have the enclosure circulating water within itself as I await my waterblock. However, I seem to be having a weird problem with my radiator. When the system is running I get this wierd, high pitched noise, and after some investigation, I figured out that it is coming from the rad. I know for a fact that it is not the fan (I turned it off, and the sound didn't go away). I also am pretty sure that it is not the pump, as I tested it by itself, and no problem. One other thing that I noticed is that if I pinch off the flow to the rad the sound is dampened; if I pinch it off enough the sound stops completely. Has anyone else has this problem? And if so, how did you fix it?

Here's how things are arranged:
ABS resevior --> Little Giant pump --> heatercore radiator (Chevette) --> resevior

well its obvious that something is vibrating or something strange when the water flows through it...

try shaking the rad violently and see if anything falls out...

Shaking it was my first thought too, but there was no rattle at all when I tried that.

Have you tested the flowrate to determine what the velocity is through that radiator? My first instinct says that you've got a resonance going that is based upon flowrate. This could either be because you're pumping too much through or because the core has some blockage. Is it used? If it's blocked then cleaning it out should help. A soak in lime-away or a weakened blend of muriatic acid should help. If you use acid, remember add acid to water to weaken it, not the other way around.

If it's because of flow, take heart as the flowrate will drop when you get a block installed. If it's purely frequency based, it'll resonate to a degree regardless of flow because the forcing function will be pump rpm. In this second case what you need to do is change the resonant frequency. This is most easily changed by using soft mounts for the radiator. (Of course, I'm assuming that right now you've got it rigidly mounted to something.) Some rubber washers on the mounts will decouple it from its supporting frame and may do the trick.

If the sound goes away significantly when you place your hand hard against the radiator, it's probably a mounting issue.

Best of luck and let us know how it goes.

myv65 is probably right.

I'd try shaking it, to get rid of air that might be trapped in the heater core: that might be the source of the noise.

Was that supposed to make me feel better? I mean, yeah, of course that's true, but one doesn't have to think about flow reductions, now does he? :D

Seriously though, I fixed the problem. I installed my waterblock (and 18' of 1/2" ID tubing), and I also added some weather striping between the rad and its housing. As I did both at the same time I don't know which has more of an effect, but I guess that doesn't matter a whole lot. Thanks for your suggestions folks.