Waaaahh Waaahh resonance? sound from new build?

[joshcloud9]

Hi there,

I just transplanted and upgraded from my beloved Lian Li to el cheapo case to take advantage of 120mm fans and normal front-to-back airflow. Here's what I've swapped out so far:

LIAN LI PC-60APLUSII >> CoolerMaster 431 Elite Plus
AMD Phenom 925 2.8Ghz (95w) >> Amd Phenom 970 3.5Ghz (125w)
ASUS M2N-E > M5A97-EVO Motherboard
SAPPHIRE Radeon 5450 (fanless) >> SAPPHIRE 6570 (w/Quiet fan)
Obviously not use for gaming!

I used an older (2008) but new OCZ 500 SXS 500w power supply that I had as a backup handy (it's black and has nice screened cables)

My problem is that having setup everything using PWM 120mm Arctic Cooling fans I have this super annoying Waaahh Waaahh sound that is louder than the fan spinning sounds.

I even changed out the power supply fan using another AC PWM and it's still doing it.

It seems like it's a resonance sound as when I change the fan speed on the only unchaged fan left (the default Cooler Master 212 EVO 120mm) it doesn't change the Waaahh Waaahh sound?

If I hold my hands against the side panels there is also no change.

I'm at a loss as to how to find out what it might be?

My Lian Li didn't do this

Any ideas what I can do to find the cause?

 

[aigomorla]

vibrations from the overall case.

Its causing the entire case to vibrate to that Waaah Waaaah noise.
Touch the case and see if u have a lot of vibrations.

AFter that i would put something heavy and insulted on top of your case to make it more rigid.
Insulated meaning.. so the object itself wont do a Waah Waaah noise.
So a heavy dictionary wrapped around a towel and then placed on top.
Then see if u still have that Waaah Waaah noise.

 

[Automaticman]

It sounds like an interference pattern between two fans that are running close to, but not exactly the same speed. If all of the fans are PWM controlled, trying using speedfan or something to slightly adjust speed of each fan, one at a time. If you get one of the fans making the noise, the time between the waaah waaah noises to get shorter or longer.

You might also be getting some resonation amplifying the effect, but pressing on panels with your hand should have helped identify that if it were the case. Have you tried pressing directly on the fan frames themselves while they spin to see if one is vibrating slightly?

 

[joshcloud9]

Thanks, I will try switching around the fans that are PWM controlled.
I only have two PWM headers on this MB, so will pair the CM 212 fan with one of the Arctic fans. And leave the other Arctic fan on it's own.

The other thing I will try is to flex mount some of the fans using two cable ties per mount hole (using the head of the tie as a stopper from pulling thru the hole, and another tie head to secure the opposite end) and a rubber pad to insulate the fan from the case.

Then I will try putting the Power Supply fan on one of the PWM circuits, currently it is running from reduced voltage directly from within the power supply. I could also try rubber mounting it but that will require a complete redoing the nice neat cable wiring job I did! It does perhaps seem to be coming from the power supply area..

When I push in the various panels the sound changes a little but is still very much present. May try some sound deadening rubber strips inside the outer panels. Have to locate something suitable...

Currently I'm running a deeptest on a hard drive, so just as soon as that's done will try it

PS. I tried stopping a few of the fans dead by pressing them near the center and the sound resolutely continued! My suspicion is leading me more and more to the power supply...

 

[Automaticman]

one trick from working on cars you can try is take a short length of hose or tubing and listen to one end while moving the other end around the PC. This can help pinpoint the area where the noise is actually coming from.