If I'm mot wrong (and it has been known) pinking is the sound you can hear when the fuel air mixture in the cylinders detonates (like a diesel), instead of burning rapidly and it can wreck your engine eg put a hole in the top of the piston! Its usually most noticable when the engine is under load eg when going up a hill in a highish gear, putting your foot down will make it pink badly if there is a problem. Common cause on older cars was ignition timing being out, with the Z I guess you could still get that but it may mean something was awry with sensor or the ecu (off the top of my head!!!)
Pinkling now, is that still legal?