I ordered a Dell XPS 13 9380 Developer Edition ( with ubuntu ) and it suffered from coil whine. The problem was reproducible. The sound appeared with AC on and battery loaded with any action ( opening software / copy / just scrolling pages ).
The sound was coming more from the upper left part near the AC.

I sended the notebook back . Would have liked to keep it cause all other stuff is nice - but the sound is pretty irritating

Hi Allen, I'm on the XPS Community Engagement team at Dell and we'd like to better understand the problem you're experiencing. If you can private message me your service tag and any additional info about the specific issue I will forward it on to our engineering team.

Thanks!
XPS Community Engagement Team @ Dell

I had a 9350 with bad coil whine and I can't believe it's still an issue all these years later.

I have same issue on my XPS15, however there's even one more source of hifreq noise: "when image on display is not static"

It would be interesting to see comparison of whine or noise between:
- displaying any document (e.g. wiki) and
- scrolling the document

In my experience this has been a problem with a lot of Ultrabook style laptops the last few years.  I actually returned an early HP Spectre because I couldn't deal with the intensity of whine it produced, the second one was similar, switched to the XPS 13 and while still present it was far less intense.  There's something in the basic design of these machines in conjunction with the power requirements that seems to make them predisposed.