Chosen Solution
I recently purchased the 2017 MB Pro 13" and saw your new teardown of the 2018 version. Had a scenario regarding the power adapter and was hoping you could shed some light. When I connect my Bose QC15 headphones to the MacBook Pro (using the headphone jack) while the power adapter is plugged in (not using the grounded extension cable), the headphones reveal a slight buzzing noise that dissipates when touching any metal part of the laptop. However, when using a grounded extension cable to connect the power adapter, the buzzing noise disappears without the need to touch a metal part of the laptop. After taking my laptop to Apple about a month ago, we tried using multiple power adapters, and multiple battery-powered headphones. When this didn’t resolve the issue, they advised that the machine was defective and to get a replacement, which I did. However, the issue still recurs with the replacement 2017 MacBook Pro I received. Here are my questions: (1) is it possible for you to recreate this issue with 2017 MacBook Pro and charger?; (2) Is this issue resolved when using the newer power adapter with the 2017 MacBook Pro?; and (3) Does this issue occur on the new 2018 MacBook Pro with the old power adapter or the new power adapter? Thanks for your comprehensive look and hope this is something your team can do. All the best!
I think you’ve already go your answer here. The difference between the duck head and the 3 prog cord is the grounding pin and its connection to a proper ground point. I’ve seen similar issues with stereo speakers when the deck was not grounded you could hear the hum of the power supply (using a cheater plug). While the new power adapter may have additional shielding, this shielding is useless until its tied to ground to dissipate the energy. This gets into a floating Faraday Cage Vs grounded Faraday Cage.
