Hi Ryan, bored again today so I spent a bit of time looking around the engine on my car, the inlet manifold is unlike anything I have ever seen its an all aluminium work of art with the Throttle valve at the bulkhead end and behind the throttle is the EGR valve this seems to enter the manifold further down from the throttle so it doesn't seem to go in on the fresh air side of the turbo pipe.
I did a bit of research on the inlet manifold it would appear there are no swirl flaps in the manifold just a rather complex little intercooler system for the EGR every thing on the manifold is water cooled and looks like hours of FUN to strip out.
With regard to the throaty induction roar it sounds like the induction pipe that runs from the other side of the MAF sensor is getting extra air from somewhere have a look at the polythene pipe where it attaches to the MAF sensor then inspect the pipe as far down towards the rear of the engine as you can, I have had this before where there is a rubber joint between the turbo intake and the polythene pipe, the rubber union had split and the car sounded deeper as you say when revved, but the easiest place to start is where the polythene pipe joins the air box as I have had problems when I disconnect the pipe to get the air filter out, the problem is that the pipe is so flimsy when you push it back on that the lower edge folds under and leaves a gap one side.
The problem is the MAF won't spot the extra air coming in as it won't register a fault because it considers it doesn't exist, the only thing that bought the problem to light was the induction roar and the fact that the car was regenerating the DPF about five times in every hundred miles as the ECU picks up the extra air via the MAP sensor readings and adjusts the fueling to compensate so the thing over fuels and blocks the DPF quicker.
Regards Steve.