I bought a Dell U3011 30" monitor that was the highest rated monitor in several reviews. It has a very slight hum.

Like most long time SPCR followers I have spent several years meticulously picking the components in my computer until now it is extremely quiet. You know the drill - fanless power supply, SSDs, Nexus 120mm fans at 7V, Thermalright True Copper CPU heatsink, heatpipes on my graphics card. As a result, the loudest component I have is that super deluxe 30 inch Dell monitor. At 100% brightness it is quiet. When you cut to 90% brightness or below the monitor hums. Spectacular display but it hums. Not a loud hum but you can hear it if the A/C and everything in the house is off.

It is still in warranty so I called Dell and bless their hearts they promptly sent a replacement. I received it today and plugged up the replacement monitor. It has the same hum under 90% brightness. Dern. I guess my project to make my computer quieter has finally come to a close...

Set the monitor to above 90% brightness, and use Nvidia/AMD software to tweak the colour settings. With some effort, you should be able to achieve reasonable colour accuracy.

The color is perfect. The problem is the hum.

What flemeister suggest is to up the brightness until the hum is gone, then use the software settings to get back the desired color levels. This works sometimes but isn't an optimal solution imo.

If possible I would return the unit and get a new one. Could be that you just were unlucky and got a lemon. Most modern TFTs (since the last generation or so) does not hum. My U2711 did not hum, nor the U2311 I switched to until I finally settled for my current U2412M, that also does not hum.
I'm sensitive to noise (had an old 2405FPW that drove me crazy) and my hearing is good but not perfect. If the current generation monitor emits noise it's below my threshold. I mean there is noise, the faint electronic buzzing that's common for a lot of electronics. It's constant at any brightness level and if I keep my ear close to the back of the monitor I can hear it but it's inaudible 30cm away.

I see. Thanks Voctnik and thanks Flemister! I'll give it a try. I have a 2711 as well. It is great and has no hum.

I have already gotten a replacement from Dell and it hummed too so I sent it back.

Thank you Voctnik! Thank you Flemister! It worked perfectly. I set the monitor to 100% brightness and then found the brightness setting in Catalyst, the video driver/control software and cut it to 50%. The monitor looks great and has no hum. Yaay!

Hmmm... my U3011 has the same problem (REV A09) so it will go back to the shop. Increasing the brightness to 100% isn't an option for me as it will greatly increase energy consumption.

It turns out 100% is just too bright for me. I leave it at about 40% and have just resigned myself to the fact that the monitor is the loudest part of my computer.

That's a shame. By the way, sorry for not making my reply clear to begin with. Must've been half asleep.

I had tried that method with my humming Dell SP2309W. However, like you, over time I found it to be too bright. Even after extensively tweaking Nvidia/ATI colour settings, the monitor still had a kind of radiant glow that made it a bit uncomfortable on my eyes.

I'm now using a Dell U2412M that's perfectly silent at any brightness setting.

I did some more searching but it seems that it's normal for the U3011 to emit this kind of hum. So sending it back is probably only a waste of money and will probably get me a kind of refurbished unit with the same problem

The brightness fix seems to be quite common for a lot of brands! For some people changing the refreshrate also works but not with my U3011.

Maybe I can fix the humming myself when the warranty has expired in 3 years..?

By the way, my Hazro 30inch didn't hum at all (but is broken...).

The problem was temporarily solved by a suggestion from Voctnik and Flemister in that I simply lower the brightness in Catalyst, the driver software, and left the hardware brightness setting at 100%. I guess Catalyst no longer controls it or something because after the last couple of "updates" to Catalyst, it no longer works.

Yes, that is some kind of workaround that works. However, it will use a lot more energy and probably decrease the life expectancy of the backlight as well.

It's remarkable to find how command this problem is when you search for it. I haven't found yet which component is the culprit. I suspect some coils from the internal powersupply? Would a bit of glue help (after the warranty has expired) in that case?