I have a Titanium 1.8 tdci and got the same message,car is working fine tho and has been for over a week,the readout pops up at varying distances e.g just out the drive or maybe after 16 miles,it does sound as if the exhaust is blowing-sometimes- but cant find any corrosion-holes etc.The read out started after not paying attention and nearly stalling it at some traffic lights.
Afgter checking on the web for days looking at stuff it would seem that even a diagnostic check might not identify the problem,which seems to be a big waste of cash
Did you get any further with your fault readout?