But you do have a dumpvalve.
Nissan decided to put a recirculating jobbie on the 'r' so you may be hearing that do it's funky little thing.
You may be hearing boost whistling back through the turbo..
If you look sort of down at the top rhs of the intercooler you should see the dump valve. There is a rubber hose sort of behind and below the top rhs intercooler hose, this comes off of the plenum to the bottom of the recirculating dumpvalve, a hks ssqv is a big silver thing, you couldn't miss it.
You may have got lucky and ended up getting a complete manifold, hybrid turbo, external waste gated beast but i doubt it :lol: