I have never heard these sounds.
The most I have heard is the cooling fans coming on slowly and the AC compressor ramping up after plugging in on a hot day, after leaving the car unplugged most of the day.
Normally all I hear when I plug in is a few light clicks and clunks as relays (?) engage somewhere...
Are all the coolant reservoirs under your hood at a good level?
If so,, maybe a trip to the dealer might be worth the hassle... Good luck with that.
Used '14 2LT w/ DCFC.
+61k miles. Only one LONG visit to the shop....
GM needs Modern Troubleshooting tools for Modern EV's.