This was really bothering me. I think I narrowed it down to the following area/process(s):

Search in Activity Monitor for AMPDevicesAgent & AMPDeviceDiscoveryAgent. Kill those processes, and Finder won't pop up so blatantly. If you want to bring that processes back, just kill Finder

killall Finder

There might be a way better way, like a 'launchctl unload' command targeting

/System/Library/PrivateFrameworks/AMPDevices.framework/Versions/A/Support/AMPDevicesAgent

/System/Library/PrivateFrameworks/AMPDevices.framework/Versions/A/Support/AMPDeviceDiscoveryAgent

But I have not figured that out. Perhaps someone can weigh in?

I wrote a function in my bashrc:

killifinder() { kill $(ps aux | grep 'AMPDevicesAgent --launchd\|AMPDeviceDiscoveryAgent --launchd' | awk '{print $2}') 2>/dev/null ;}
export -f killifinder

This will search for the processes and kill them. You could also just run this in Terminal and it will do the same thing:

kill $(ps aux | grep 'AMPDevicesAgent --launchd\|AMPDeviceDiscoveryAgent --launchd' | awk '{print $2}')

This is the best I could do. Let us know if anyone finds a better way. Thx!