The first thing I would do is run a basic boost leak test. Build your own tester out of rubber IC pipe and a pvc end cap, drill and install a valve stem in the end cap and bolt this up to your turbo. A "how to" for this can be found here. Basically you will be pumping air through your entire intake and listening for leaks, fixing them as you go. I would do this at least once a month as basic maintenance procedure. The second thing I would look into is your wastegate. It sounds to me like you either have a really bad pre turbo exhaust leak (which you would hear from driving so I am ASSUMING this is not the case), OR your wastegate is stuck open. Check your actuator arm and see if you can move it back towards the actuator. If it is getting stuck open then your exhaust gases are passing directly into your exhaust and skipping the turbo entirely. (Path of least resistance) If this is bad then you will probably need to replace the actuator. Also, this may sound funny.. but when you have the intake off to put on the intake tester, make sure your turbo still has clean/sharp looking blades on it.. If not, this is very bad