Whenever I start my explorer after it has been sitting for a while it makes a loud pinging noise for a couple seconds. I can also hear it when I'm accelerating or going up hills, what could be the problem? Could it be a timing problem?
sounds like "labor knock" or pre-ignition. this is caused by low octane fuel, OR if you have over 100thousand miles on it you should change the spark plugs and wires and maybe put some fuel treatment in it, usually the computer compensates for preignition on a newer vehicle like yours, however if the plugs are shot you need to check and change them out. try that.