Pinging, or detonation, can be caused by several things, as well as fuel quality. Dan mentioned what is known as the knock sensor, which could very well be the problem. It's job is to sense pinging, or engine knock due to timing, or any other issues, and retard the timing accordingly, until it no longer senses the knock. I would definitely find someone to pull the codes, to see if it has any, and what they are. Knock sensors fail usually due to mechanical damage(someone breaking the connector, or something like that), but they can just take a dump for no reason.
A malfunctioning EGR valve can also cause the pinging, as can too much heat(overheating), carbon buildup on the tops of the pistons(pre-ignition), or a really lean fuel mixture.
I'd suggest seeing if there are any codes stored, and go from there....and possibly throw a can of Octane boost in it for now.... :yes:
Randy, what model is this? Q45, 35? I'll pull any TSBs it may have for ya....