When I accelerate there is a rattling sound could that be my engine? on 2006 Ford Explorer

It varies when it happens

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2 answers
Give better description of when it happens ....cold start-up , after warm on hills , accellerating on turns,Sitting still in neutral giving it gas? in drive with foot on brakes while giving it gas ....ETC. get my drift? ..WHAT's "the variable" in "it varies when it happens" thanks.
Need more info. What is the 8th digit of the VIN number?