Ah, Netflix plays that blaring music/trailer stuff at you–but only on certain Roku boxes, like the Roku 3 I have.
It did NOT do that on the Roku TV I had for a little while, nor does it do that on my Fire TV boxes or via my web browser on my computer. I actually left my long-term relationship with Roku for this reason. I was on the verge of dumping Netflix because of it when that behavior began.
No, you should direct your annoyance at Roku because this is clearly their initiative.
I did find it interesting that clearly the Roku TV I had was filled with Roku guts that were too weak to support that nonsense. I gave that TV away. One is far, far better off buying separate TV and smarts.
So anyway, screw Roku for insisting that their boxes blare at you for no reason, to try to imitate turning on a TV in the 1970s when it just makes noise at you from the get go. They think that a silent screen is a turn off. Little do they know.