What engine are we dealing with here? I notice both of your trucks in the gallery have V-8's in them. The usual way to isolate a noisy piston is to short out spark plugs one at a time and see if the noise changes with the cylinder not making power. A loosely-fitted piston will usually quiet down noticeably with the ignition disabled to that cylinder, while a loose rod bearing might change note to a double knock with power off the cylinder. Main bearing noises or valve lifter rattles don't generally change note when the ignition is cut off.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!