Hyundai i30 2009: Engine making a pinging noise

If it's pinging all the time, there's something wrong and it needs investigating. If it's only there when the engine is under load, like accelerating or climbing a hill, it could be a transient thing while the engine adjusts to the new conditions. Today's engines are dependent on electronics and there is little that can be done to fix a problem like pinging, you can't swing the distributer a few degrees to get rid of it. It could be a sensor that's on the wrong end of the spec band, or the timing could be marginally out. Using a higher grade fuel is quick fix that might work, but of course it comes at a cost at the pump. If he's really  concerned about it take the car back to the dealer and insist that it be fixed. The company recommends 91-octane fuel and they should be held accountable for ensuring that it will.