RX7 Turbo problem

This Mazda RX7 came to our shop by recomendation of Mazda Dealership. He has been having problem on poor or no turbo-action for last 3 years. Mind you that he drives less than 5000km per year only during summer time.
 I road tested with him and if you drive normal, you hardly feel the turbo boost, but when you drive harder, then you will fell the turbo boost(not as good as it should be), and associated with hissing sound at end ob boosting.

We needed to test all the components, like waste gate, charge relief valve, actuator control,,,,. All tested well, and other than turbo every thing works fine. When I started take apart the piing, induction tubing, I could not see any problem, Reassemble again, go on longer road test. The next day I use the stethoscope to listen the source of the noise. It sounded like impel la touching. The high pitch noise simulate metallic noise? After rechecking again, I found the small crack on joint tubing just above the hose clamp. That was it, the car is fix, and it runs very well, it has a lot of acceleration now. I just wanted to share this repair incident.