Sounds like it may be detonation. But the only problem I have is that detonation usually occurs with a hotter motor, not a cold one  Are you running higher octane or colder plugs with the bumped timing?
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'97 T-bird LX 4.6L 2V, auto
SVO heads/intake, Vortech T-trim, front mounted intercooler, blower cams, Cobra crank, Manley H-beam rods, JE pistons, Aeromotive fuel system w/ 42# injectors, and much more
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