Get ya an oscilloscope & keep it on hand for when you do hear the noise. Try & pinpoint for sure the certain area you hear it..I know its difficult with all the other engine noise, but thats what youre going to have to do unless you get lucky one day taking it to the mechanic.
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1998 Pontiac Grand Prix GTP
F-Body Ft Brake Upgrade, CAI, Buick STB, 226k miles & counting, otherwise stock