I listened a few times with headphones and volume at max (be sure to stop before 1:31 if you attempt the same, as the gunshots are deafening).
I hear the rustling sound punctuated by a voice and, later, by music. I agree that this sounds like a morning radio or television show because I hear the phrase "It's ten to seven" (~30 sec. mark) which squares evenly with the known timeline.
The rustling sounds are less identifiable. I don't have a Ring/Nest, but do have a similar device, so I took a listen to some of our previous recordings. I get a similar-ish sound when we have a large appliance running, like washer/dryer/dishwasher. Because it's not a consistent sound (it's conspicuously absent in the moments after the shooting), I think something with a timed cycle might fit. Heck, it could even be a heat pump for an HVAC system turning on and off.
Regardless of origin, this sound does make it quite difficult to make out what's said once the conversation begins. I hear a distinct and chipper "Good morning!" followed by what sounds to be a male voice. This second voice, to my ears, sounds more similar in volume and direction to Liz's voice (as in, not similar to the radio/tv). I see some movement on the video, which appears to be the shooter's left arm, then a startled gasp and "What?!" from Liz.
The last time the second voice speaks, I hear something like "you were right, it's not." The first time I listened, however, I thought the shooter said "you're going to die, today." After a few more listens, I think that was my confirmation bias at play.
I have some more general thoughts, but I'll put them in a second post to not derail this conversation.