2001 gt pinging

i need help .... the car will not do this when it is cold but when u get it hot start in 1st gear slowly speed up and when u get around 2,000@3,000rpm the motor will sound like little machine guns, a faint pinging noise nothing like a rod or the bottom end of the motor and if u flutter the gas between those ranges same thing but not a constant noise just between those rpms the car has 56,000 miles on it !!!!!!!!!