Teach it to whistle your favorite tunes
Slightly loose carb bolts (as mentioned in above post) or a vacuum leak somewhere can cause the whistle.
History (or trivia which you probably did not wish to know):
In the early days of motoring, many cars whistled. Hudson had a carburetor manufactured for them by Detroit Lubricator, which was basically a rip-off of the S.U., that had a triangular air intake. This stopped the whistle, and Hudson started advertising the car as the "Silent Six".
Jon
