The small hose is a vacuum pipe to pull the dump valve open…it must be blocked off.

the chatter noise is the compressor wheel stalling against the built up,pressure when you close the throttle.

you may need a smoke test to rule out any leaks. You will hear turbo whistle though as that is the boost pressure building, they will always do that.

Do you have a boost gauge to check it is creating the required pressure and not venting somewhere like a split intercooler.