While accelerating or going up hill the engine pings or rattles. It also heats up. Engine heat use to be stable at the botto of scale, but now it runs at mid scale and swings from half to 3/4 of scale.
Pinging can be caused by a hot running enigne, you'll need to start by checking the obvious causes of overheating on these, which would be the engine thermostat, the fan clutch, and blockage in front of the radiator. It's very common for dirt, dust, and leaves to build up in front of the radiator and behind the a/c condensor which will result in low airflow through it. Also, check the level of coolant in the radiator.