Well not heard of this one before but if I were hazarding a guess I would say its almost definately coming from the turbo or more so the associated pipe work.
In the turbo system you have blow off valves, some hiss, some parp and it sounds like yours are wedged open.
First thing to do is get it up on a ramp and do a thorough inspection of all the pipe work, squashing them and looking for splits or even a pipe that has come adrift. Then have a look at the pop off valves. Also on the turbo they have actuating rods, make sure these are not bent or seized.
Also check the pressure monitors that are screwed to the inner wings and have a small air pipe going from the front to them. I think the drivers side one is behind the header tank so you might have to remove it. If you do make sure when you refit it, the pipe at the base of the header tank is very secure.
You might also want to listen under the plenum for air leaked. The 3200 has a habit of working the screw loose on the belly plate then sucking the gasket in, but this would usually be accompanied with wild idling.
If you still can't find anything, take it to your nearest indie, where abouts are you?
Ps. Great lurking, joined a year ago, this is your first post.....we don't bite, honest!
