I have a 2005 156 1.9JTD 156 16v and noticed a rushing air sound over the last couple of days. It specifially happens under accelaration (even ot low speeds) and is louder the more agressive I accelerate.
I saw the same sort of problem on a Skoda Octavia vRS. One of the hoses going into the plenum had come loose, so air was being forced out when the turbo spun up under acceleration and being sucked in when the pressure in the plenum was below atmospheric. You noticed any performance problems?