help on knock knock noise

i have a 5mge supra. n its a 85 supra. i have a question about my supra. when i start up the car and its operated. i keep hearing a vibrate noise came out from between the egr coolen valve cover thats the one that on the back of the engine its kind of square. have i think 6 bolt on it. i keep hear a vibrate noice came out of that.... so i dont know is it air leak n thats what it cause that or. is it my valve or my piston is knocking. i only hear this when i step on the gas. if i release my gas pedal or when i accelerate the speed and it keep having that weird knocking noise tho n i not sure is it just a vibrate noise or is it my valve. so iono. and if i didnt accelerate or step the gas pedal to make the car go or move then i didnt have this weird noise. but when i step on it it keep making that noise so iono. any suggestion.... please help this is really bugging me....