2002 Jeep Grand Cherokee ticking noise

2002 Jeep Grand Cherokee ticking noise
I have a 2002 Jeep Grand Cherokee with the straight six, there has been a tapping sound coming from under the hood, it comes and goes. Sometimes when it first started and sometimes when it's under a load, like going up a hill. I've tried using a higher octane gas and it seamed to help but it came back. The engine has 165,000 miles on it and has been serviced regularly The noise is coming from the drivers side of the engine compartment.