I got a Dell U2412M (24", IPS panel, 1920x1200) about three months ago,
and I'm very pleased with it. Absolutely silent, as far as I can hear!
Is that across all of the brightness range? I did look at that monitor and also the U2312HM, although I couldn't find much about noise (or lack of) on the U2312HM. I do like the Dell monitors, my 2209WA seems well built, it's just the annoying noise that it produces on anything but 100 brightness that is making me consider a change.
I have a 2209WA and U2412M. As you say, my 2209WA also makes an annoying noise. I've never noticed any noise from my U2412M, but I just compared the two with my ear up to the top-back of both. It appears there's some noise coming from the U2412M, but only very slight. The 2209WA is significantly noisier, and also more high pitched in tone.
I've been very happy with the U2412M.