PSU or case hum.

[Miniamba]

Hi!

First off sorry for my English, it's not my native language.

Now to the problem - my computer produces a low periodic hum,
which repeats itself every two-three seconds. It's not very loud, but still irritates me.
Also I should mention that it occurs even when the system is idle.
First I thought that it could be the PSU fan, so I replaced it with a new Arctic Cooling fan, but that didn't take care of it.
Then I read a bunch of articles on the problem, but none of them offered any logical solutions, except one where someone
suggested that because I have two HDDs their rpms might be a little bit off and that produces the hum, since
they are both connected to the same piece of metal.
I disconnected one and the hum was indeed gone.
Then I reconnected it, but put so that it wouldn't touch the case - the hum was back.
The PSU is Chieftec 550W running a regular motherboard, 1 physical CPU, 2 ddr2 sticks, 1 9800GT, 2 HDDs and 1 5-in-1 card reader. My guess is that the
power supply should be enough.

Any thoughts?

 

[Aastii]

Holds your hands on the each side of the case and press gently, as though you are trying to stop the vibration. Rub down the side, especially around the edges, and see if there is a point where the the "hum" stops. If it does, it is one of your case panels vibrating against the main chassis of your case

 

[linkin]

It's probably the hard drives making noise (if you have more than one)

 

[Nanobyte]

The difference in HDD speeds is an interesting suggestion. That would be just like tuning a musical instrument such as the piano where a note and a tuning fork are struck at the same time. If they are slightly out, you get beats. The tuning tech changes pitch of the instrument until they get a constant tone. Dead on, or way out, there are no beats.

If that is the cause, you could try moving the drives further apart (if feasible). Taping on a small weight or jamming in some dampening material such as closed cell foam may help, even if only as an experiment - making sure not to affect cooling. You can also simulate using your finger as a damper on each drive. Per Aastii, the situation could be exacerbated by the case acting as a resonator.

I get an occasional periodic vibration when my very old, worn PSU fan has a bad turn. That is probably worn bearings that vibrate at certain temperatures.

To isolate the source, use the cardboard centre of a toilet roll or paper towel roll - one end up to your ear and the other pointing at suspect areas.