If you're sure it's not something else (turbo itself, powersteering pump, something else that could make the noise?.) you could spray some soapy water on the pressure side of the turbo and further to the cilinderhead. Don't forget the EGR pipe and joints.
Let some one rev the car, i know it won't raise the boost that much this way (i could hardly reach 0.1 bar boost this way) but maybe it's enough to see something bubbling when you look under the hood when the engine is revved.
Maybe there 's a smarter and easier way to detect leaks but i don't know how,
I assume the woosh is the same in all gears when accelerating?
Classic sign of a split intercooler hose.
Check all pipes from the intercooler to the turbo inlet.
1.4 TDCI doesn't have an intercooler so it can't leak either ;). From about 2000 rpm the boost really builds up, under 2000 rpm there's not much done.
Only thing between you're turbo and the inlet is the resonance box, a piece of rubber hose, and if you have it, an throttle valve and that's it. The other thing connected to the high pressure side of your inlet is the EGR pipe.
In between the throttle valve and EGR connection there's a little hose connection to the pressure sensor. The connection between the small hose and the inlet is only visible when you remove the upper plastic part guarding the timing belt.
Not al models have a pressure sensor and throttle valve, don't know if there's a specific date or as of VIN number or that Ford just took what they had lying in the shelf. Heard the last thing is the Ford "logic".
I dont think theres really a way to set up a louder whistle, short of changing and adding a dump valve to make it louder?
Barry, did you get any further with this?
Ouch, nights are not fun at all!
Sorry to pop in, have the complete opposite problem to the OP.
I actually like the sound of turbo whistle, how can I make it audible in my 1.4TDCI ?
If you fit performance mods/ parts, (remap/ tuning box, air filter, exhaust etc), it can often give the car a more sporting/ louder sound, a mechanical boost gauge connected to the compressor outlet can sometimes bring the turbo sound into the cabin
For what i've read a worn turbo has a more whining sound, not wooshing. But (luckily) i don't have any experience with it so it's just from hear say.
Wooshing, like the blower has come on, like you describe still sounds as air escaping somewhere. But i assume that if more then one mechanic has looked at it they checked all possible connections etc. where air could escape. (And cracks).
So if the sound is bearable and the engine is running fine i wouldn't worry to much. (i know, i would want to know what it was if it was my car ;))
Om an other note, the fact that the car runs fine doesn't exclude the possibility that there's something not quitte right. My EGR valve was leaking, internally so the boost went right out in the exhaust, but the car ran fine. Only after i completely blanked the EGR i noticed the even more faster rise of the boost and the car ran even better. Problem is that if you have no comparison it's hard to tell.
If you want to know what the car is doing (or to detect any problems) it might be worth investing in a blue tooth OBD2 dongle (about 10 euros from China) so you can see all the info (boost, MAF and a lot more sensors. And you can even reset error codes so that's also very convenient) from the car on your android phone with Torque Pro.