Title says it, didn't used to happen but now when you romp it, it sounds like a can of marbles until you let off :P

I know this is an issue that shows up over age/maintenance periods, what is usually the cause(s) of it?

 

Low octane fuel or too hot of a plug. Try a higher octane fuel.

 

Or blown plenum......

 

Look up plenum gasket issues. See if you have more symptoms.

 

I get engine ping when I don't travel at highway speeds for a while due to carbon buildup in the combustion chambers. Sometimes it helps to use a gasoline additive to prevent that. Going to a less restrictive exhaust helps also.