Monitor is causing hum in microphone recordings.

[LokiNya]

I've recently bought a dynamic microphone and mixer and connected it to the line-in of my sound card. When I'm playing back what I've recorded, I can hear an annoying hum.
So I tried to track the problem and it seems the hum is gone when I turn off my monitor.

I don't have grounded wall sockets in this room, so I connected everything with an extension cable to the grounded socket in the bathroom. Sadly, the hum wasn't gone, and I gained another hum in my speakers when it's grounded.

Has anyone here maybe some ideas on how to fix this?
Would a "Ground Loop Isolator" between mixer and sound card help? Or some of those ferrite clamps on cables?

Here's some more info.
Microphone (Shure pg48) is connected to mixer (Behringer Xenyx 802) and the mixer goes to the line-in of my sound card, and from my sound card output an amp with a pair of speakers.
Monitor is a SGI GDM-FW9011 24" CRT

 

[BakedA|aska]

A ground loop isolator wouldn't be a bad idea. What would really help, I think, is a power conditioner. Ferrite beads wouldn't hurt, either.

LCD monitors all have one or more small fluorescent tubes, which requires a high voltage ballast circuit to be driven. To me, it sounds like that ballast may be "leaking", causing the EM interference you're hearing.

It's either a leaky ballast in your monitor, or an issue with EM noise in your home's electrical wiring. Both problems are usually fixed by isolating ground, and conditioning power.

 

[LokiNya]

Thanks BakedA|aska.

I don't have an LCD monitor, but a CRT (there's a topic about this monitor here)

While recording I moved my microphone a good 2 meters away from my monitor, and the hum was gone, so doesn't look like the interfering signal is traveling through the cables or a ground loop, but some RF interference or magnetic field that my monitor is creating or something.

Hopefully, it's the cable that picks up most of it, then I guess a quick fix are some ferrite beads on the XLR cable, or make a heavy shielded cable myself. If most of it is picked up by the microphone, which is more likely I guess, I'm not sure what to do.

 

[BakedA|aska]

Thanks BakedA|aska.

I don't have an LCD monitor, but a CRT (there's a topic about this monitor here)

While recording I moved my microphone a good 2 meters away from my monitor, and the hum was gone, so doesn't look like the interfering signal is traveling through the cables or a ground loop, but some RF interference or magnetic field that my monitor is creating or something.

Hopefully, it's the cable that picks up most of it, then I guess a quick fix are some ferrite beads on the XLR cable, or make a heavy shielded cable myself. If most of it is picked up by the microphone, which is more likely I guess, I'm not sure what to do.

The fact that your monitor is a CRT probably has something to do with it. If I had to venture a guess, I'd say the flyback transformer or the circuits ancillary to its operation are leaking. What sort of pitch does this hum come in at? I'm assuming it's not 60hz.

 

[LokiNya]

Hmm, If that would be the case, I guess it will involve replacing parts? Any way to confirm if that is the problem?

Here is a short recording I made on a high volume. It begins with the monitor on, then you can hear a click. That's me turning off the monitor and later turning it on again.
You can also hear some static, but that's only noticeable at these volumes.

http://www.megaupload.com/?d=162LP7G3

(sorry about the megaupload, can't access my ISP's webspace atm.)