Thanks for your reply, is there no way to dampen the whistle or cut it out?
Put the standard intake back on.
Seriously though, the reason that the aftermarket intake is so noisy is because it is designed purely for performance. The standard air box/filter is restrictive as it is a compromise. Most people don't like their cars to make weird noises so VW designed the intake to be quiet and of course cheap to make. The routing helps to baffle the noise but also restricts airflow.
The CAI has a big hollow pipe with effectively an open end, air passes through easily and so does sound! Think of it as a didgeridoo!
Most of the time I quite like my P-flow but there are the odd occasions I wish it wasn't so noisy. It's staying because of the performance benefits.