i use it for audio as well as gamedev and even though i will often have it hooked up to a proper soundcard once i replace my firewire one, i still need to plug in quality wired headphones on the go, just as an example. my iphone and 2012 macbook pro exhibit no audible noise plugged into the same cord (all on max volume.)
after a bit more digging i've found the source of the noise to be when the USB-C -> Displayport cable is plugged in. so that means it should be ok on the road at least as i probably won't often be plugged into a screen.
it doesn't matter if the USB-C -> Displayport is on the other side from the headphone output, it seems the signal of the thunderbolt bus is getting transferred onto the audio path somehow. so if it just shielding as you say, it may not be fixable.

i will consider another cable... so many new dongles and cables for this new machine haha

at least i have an avenue to explore i guess.
no audio stutter / corruption since the update (6 hours or so uptime) which is something! i do think the DAC sounds noticably worse than the 2012 though.
the game i'm working on seems to run choppier. i've noticed that, even at the same resolution and settings, i'm seeing worse spikes in Metal on the 2018 than on OpenGL on the retina 2012. hopefully it's just the update 'settling', but it was doing this from time to time before. it's as if this machine is constantly fiddling around with its settings to manage thermals and it causes spikes here and there where it jumps down in speed. not ideal for gamedev ... my 2012 was def more consistent, though it did drop a few fps below 60 in the busiest spots, this one manages those spots, but has consistent spikes. all this for a couple of mm of thickness.
i also don't think we'd be seeing half these issues if it wasn't for the T2. i don't even like the touchbar, will never use it unless forced to (having tried in earnest) and wish i could remove it as it causes more errors than correct entries in my workflow. it's draining battery, causing complications in the software, making keyboards less repairable, slower to achieve the same functions as before, lacks haptic feedback. the additional security layers i can take or leave tbh. the SSD speed is welcome but i doubt i'd notice the different with one half as fast.
sorry i know it's not the exact thread for this full review but it does relate to the issues seen which are hopefully being patched in this update.