Audi A4 Problem Need All The Help Please ,lifters

hello i have an audi a4 1.8t 1997 , i just rebuild the whole motor, turbo and head and new oil bump..... i need some help...... i have a tapping noise at the front of the motor........it sound like a desiel.... but every thingits new and all.......the first time i got the car started the noise was loud.....and i kept it at 2500 rpm for 5 min it quit it down , buti still have the tapping noise still i xcan hear it help me tell me how to fix it thanks hani