I have the iPhone 7 Plus 128GB (AT&T). Got it Day 1. The Bluetooth drops out all the time in my 2011 Prius. It happens while listening to the Podcasts app (streaming and downloaded podcasts). It happens while listening to Music (downloaded music, using Apple Music, and using iCloud Music Library).
Often it is a half to a full second of silence. Sometimes it will cut in and out 3 or 4 times in quick succession.
It seems to be worse when I have Facebook, Slack and/or Google Maps on in the background. I've taken to turning off all non-essential apps while listening as a test. I will just leave Reminders, Safari and the audio app open. It hasn't completely eliminated the problem, but it does seem a bit better.
I was about to take the phone into the Apple Store for an exchange, but the release of iOS 10.2 (and its mention of improved BT) convinced me to wait a few days. It hasn't helped, and I'm considering taking it In tomorrow. But after reading the last few pages, it doesn't seem like it will help either.