4 Wheel Drive/SUVs: Engine Rattle/Ping in 2002 Mercury Mountioneer, mercury dealer, octain

Question
I puchased a used 2002 Merc Mountaineer(V6) with 38,000 miles.  I am experiencing a rattling sound when accelerating with a warm engine. The dealer (not a Ford dealer) has checked the engine,found no readings out of order, and has recommended using a higher octane fuel.  My owner's manual recommends a 87 octane fuel so I question why a higher octain is necessary to eliminate the rattle?  I have filled the tank with a 93 octane fuel and added a gas additive made for cleaning carbon deposits but have only driven 20 miles since doing so with no reduction/change in the rattle.

Have I not allowed enough time for the higher octane fuel to rectify the problem.  Can you think of any other solution (adjustment and/or part replacement) for this type of problem?  

Thank you for any help you can offer!  

Answer
Hi Tom and thanks for the question.  I am not a mechanical person but in my background "pinging" was normally due to an engine being out of correct timing or using the wrong gas octane.  I think the newer vehicles are computer controlled.  Drive it a few hundred miles and see if the higher octane and additive cure it.  If not I would go to a Ford or Mercury dealer and at least talk to one of the service advisers.  Best of luck,Bud