I agree that this could have been handled differently from the start, but that's done now.
I'd wait a week or so and then knock on their door or call and start by saying we seem to have gotten off on the wrong foot, can we start over. If you get another rant, then give up. If they are civil, then you can say that there seems to be some noise around 6 in the morning, what do they think it could be, and go from there.
Personally, if I got a rant after a second, in person, visit, I'd make sure to be noisy right before bed, in the hopes they'd be tired in the morning and sleep in, but that is definitely not a recipe for harmony with your neighbors.