It’s a pinging and not a tapping right? Reason I ask is because in my experience pinging is more associated with carburetion. But yours is probably fuel injected
when the problem began over a year ago, I upgraded to 89 (from 87) octane exclusively - which seemed to work for a while. But then even with that higher octane, and occasionally I'd put in super, it made absolutely no difference.
Yes, it's fuel-injected, and is definitely a ping (dealer describes it that way also).
I have no idea what the next step will be. Dealer said they'd be getting in touch with GM techs.