You could hear the whine from across the room a few seconds before a call would ring through.
People always asked how I managed to answer the phone so fast. Electromagnetic Supplementary Perception, of course.
It was clearly electromagnetically "noisy", but I do't recall ever having heard any on my phones make any unexpected audio noise... (My old-and-abused rock concert and motorcycle weary ears probably can't get up as high as inverter whine any more though...)
Also, GSM phones used TDMA (keying the transmitter on and off to occupy one of -hm- eight, I believe - time slots on a given channel.)
This is practically asking for EMC issues.
LTE, on the other hand, transmits continously (I believe - I do not work in RF engineering anymore, but try to read up on new tech every now and then.:) - much less interference-causing than the constant on/off of TDMA.
Some were barely noticeable, while one in particular (a Droid Turbo) was so loud I could hear it getting ready to receive a call from another room. This was regardless of whether they were plugged in or not, although charger whine was its own separate issue.
Thankfully it does seem to be getting better over time- my current S8 is, as far as I can tell, genuinely silent.
There's a TDMA modulation frequency at 217Hz and this interferes with all sorts of nearby audio devices. CDMA and WCDMA phones have a much broader interference spectrum, which is why you don't hear it much anymore.
I considered returning it, but I find it charming. I miss the days when you could tell exactly what your PC was doing by all the sounds it was making, and I find dead silent electronics to be elegant but a little sad.
The easiest way to experience this is to plug in headphones and hear the clicking before/after a sound is made.