Congrats and thanks for sharing! I was also shocked at the low state of charge on delivery. No chance to take it for a serious spin after getting it without a lengthy charge first! As if the Teslanxiety wasn't bad enough to begin with.
That rumbling was the indicator that you were about to cross a lane without signaling and it was just warning you, but then you've been driving this for about a month now so you probably know that by now.
Enjoy!