I have replaced my M16, which also has this noise. But I found that all I had to do was turn off C-state control in the Bios and the noise went away. Bro I highly recommend you try this. You can Google where the switch is on the Alienware Bios page. It's simple.
My m16 R1 laptop makes electronic noise when it's charging and I'm pretty sure it's not the noise coming out of the speakers. I also changed the power adapter and used outlets in different places, but the problem persisted. The noise only occurred when I was using and charging the laptop, and was completely absent when I turned it off and charge or use battery mode. Sometimes the noise is small, but most of the time the noise is perceptible. Could this be a Bios problem? After I updated all the drivers and windows patches the problem continued and my Dell service has been running for almost 10 days but the problem has not been resolved.
m16 R1, electrical noise while charging