Convinced my '08 CTS-4 pings, but dealer said, "No"
 

I'm convinced that my '08 CTS-4 (3.6L v6, Automatic, 65K miles) pings after it's warmed up, but...

I had the Greenwich, CT dealer check it out and they said, "No; it conforms to OEM spec's." I found the response too clinical; hence, I don't trust it.

It doesn't ping when it rains.

I hear it best when I drive along side a concrete wall that reflects the sound, when I hit the gas (accelerate).

It NEVER pings in neutral; I suspect it's only under load. It does NOT ping when cruising at any speed, as long as I don't accelerate.

What does it sound like? Well, because the car and engine compartment is so well insulated, it sounds like Spanish castanets. It's not as evident as it was in my '74 350ci Nova, '81 4cyl Mustang and '82 8cyl Riviera.

Anyone know a 'really good' mechanic/garage/dealer in NY/NJ/CT/PA area that can confirm 100% if I'm just hearing things?

I love the car and want to avoid any further damage; hence, I've been driving my '06 Grand Caravan SXT.

Thanks for your help!!!