Blowing sound under acceleration, mk3 Mondeo st tdci

[Bobfreckle]

So.....

I have a 2007 Mondeo ST tdci, I'm experiencing a deep blowing sound under acceleration as if the exhaust is blowing, no real loss of power but its not what it should be, I'm also not getting the pull I should in 5th/6th, recently had a new boost pipe fitted and that's when the problem started,  had the full exhaust off and its fine (less than 12 month old) checked the boost pipe is on properly and everything seems ok, I'm thinking it could be an air flow problem but when I reset the ECU the car runs like lightening.... responsive, quick, clean, but only for 2 or 3 days then its bogging down again.

 

Any Ideas???