This is driving me absolutely insane. I have a Galaxy S8 with Andriod version 9 and my bluetooth headphones are Sony WH-H900N. Basically, my phone is on silent, sitting on my desk, while I'm listening to music and for every notification I get my phone vibrates (while it is on silent) and a tone plays in my headphones. I don't know if it's something on the phone, something with the headphones, or something else. I thought it was something that had to do with Google Assistant, as occassionally, after receiving a notification, a voice would come on and say something to the affect of "When you receive a notification, press -" and then it would end. I think it has to do with the Google Assistant, but I've turned it off, as far as I can tell, for bluetooth devices. But it's still going. Any ideas?
I literally have the same problem. Same phone, android and exact same headphones, even the same settings. Did you find a solution? I only realized this a few days ago, never had problems with this before. The only solution that works for me so far is turning on the "do not desturb" mode.