Is there a flapper valve or something in the turbo system that could make a chattering sound? here's the problem. When I step on the gas, I hear the trubo spooling up, as the boost increases something starts making a clackety clack sound and there is a hesitation, kind of like missing in acceleration. If I let off the gas and drop the boost the sound disapears.

 

Something wrong with the wastegate I'm guessing.

 

check for shaft play, your turbo may be toasted

 

Detonation? How much boost? What mods?