I'm on my 2nd U2414H now and the problem just came back so I'm thinking it's a firmware and/or electronics issue.
Basically I have the sound going from my Mac through miniDP to DP (supplied Dell cable), to the Dell U2414H and out the 3.5mm socket to my 2.1 setup.
I did some testing previously with headphones, and different sound outputs on the Mac, to make sure it wasn't another device causing it, but the only way to fix it is to cycle the power on the Dell monitor, and it only occurs on the Dell monitor output.
Any ideas to solve this? I could run the monitor on the HDMI input, but it's not really solving the problem. It only seems to happen on the DP input.
Also, if I buy a U2415 or U2715H to add to the setup, I'm hoping they don't have this problem too, as I want the same setup there. It keeps my headphone port on the Mac free and allows me to switch inputs on the monitor while retaining sound output to my speakers. It's what the monitor was designed to do.
It's really intermittent, it only happened once on this new monitor (10 mins ago), but the old monitor did it much more frequently.
Thanks in advance.
I am not sure if I am having the same issue but my U2414H has similar problem with making noise from monitor audio jack when monitor is connected via DisplayPort.
I returned my first monitor as well thinking it was defective but had same issue with the replaced one.
Headphones or speakers connected to monitor audio jack makes clicking noise when its starting making sound. I am not sure if sound itself has some kind of standby and wake up cycle. I guess it only happens on its wake up cycle.
Tested this with multiple DisplayPort cables, speakers and devices with Windows 7, 8.1, even Technical Preview.