have a similar thing on my 16v jtdm, had hoped a cambelt, pump, etc would cure it and also i had a de swirl flapped manifold fitted at same time.
after a couple of drives its still there?
i only really get it on the same stretch of road when i first accelerate from coldish(which is why i hoped the new inlet manifold would stop it, incase it was leaking with swirl flaps in full open position etc ) as once its sqeeled(also i also thought boost leak sound) it then is usually not heard again in that journey(and i know it holds boost well and checked for leaks).
it always sounds near to the back of the steering wheel/dashboard corner , which is why ive not looked at turbo or exhaust manifold.
i suppose it could be a exhaust/turbo leak sealing once warm, it just doesnt sound in that area.
i might have a look at my map sensor o'ring as thats been in/out a few times it would fit that area sound wise.