out of nowhere my XL bursts into song.

What was it singing? Show tunes? Classic rock?

Had you set any alarms or reminders? Asked Assistant to sing you a song?
 
a newer pop song, I'd guess. I'm not that current with songs.
Happened a few times first day of activation. [yesterday]
Got update this morning happened again afterward.
Weird, might/must be a setting on my phone.
or a bug.
 
a newer pop song, I'd guess. I'm not that current with songs.
Happened a few times first day of activation. [yesterday]
Got update this morning happened again afterward.
Weird, might/must be a setting on my phone.
or a bug.

Keep an eye on it and see if there's something that commonly happens or you're doing when it happens
 
That's a strange but interesting happenstance, OP! Is it the same song that plays each time, or something different?
 
Transferred data from old phone to new.
Old phone had various tunes I bought over the years.
A few were free downloads from Google.
they are the newest.
.
think it might be the same one.
Not sure.
 
Maybe it's just happy. Isn't that how it works? It's so happy it can't contain itself anymore and busts into song.
 
One good reason for NOT importing from an old phone, especially one with an OS which is more than one generation back, is that you often end up with some incompatible apps, corrupt settings, or apps/settings that worked with your old OS but not so well with the new.

It often takes days or weeks to get this stuff sorted out.

Been there; done that. :)