i have a1995 502 EFI that has not ran in 4 years and when we fired her up today for the first time there is a loud rattling noise coming from the motor. when we idled her up the noise went away.... any suggestions on what it might be?

If you didn't prime the oil pump before starting the engine after 4 years the lifter would have bleed down . The rocker arms would then be loose and make a loud rattle noise until the lifters pump up again from oil pressure.

Flappers in the exhaust tips.

what griff said ,but the flappers he is probably refering to are in the exhaust y pipe