Backfiring could be cam timing off. Cam timing off, would be rough running cause if it is off. We don't know that, but pulling the valve cover is the only way to know.
You don't remember hearing such noises before, when it was on the road?
I know you've heard the cam chain rattle before, so I assume this is a different sound?
I'm not sure where to go now except to trailer it to your man and have him look it over.
From your earlier description of what happened on the trip home that day, the symptom was sudden, not something that built up and faded in over time. The chain skipping a tooth would be sudden like that.
****, I hope you're not the first double-grenade. Geez, Mike.
On the bright side, it's still running. And other users have reported one-tooth-off timing and been fine after correcting it.
BTW, don't run it any more until the cam timing has been checked and the tensioner has been verified as OK. Goes without saying, I hope.