I'm getting a whistling sound when driving in my '94 Cutlass with the 3100
V6.  It sounds like an air leak and I just can't find it.  I've pushed and
pulled on every air hose I can find with no results.  The whistling seems to
happen only when there's no throttle input after accelerating, until the
engine slows back down and goes as follows:

- The whistle almost sounds like a tea kettle.
- It only happens if I'm accelerating and let off the gas, lifting from a
steady speed results in no whistle.
- The whistle goes on for 2-3 seconds and stops, starting with a high pitch
and lowering.
- If I hit the gas again while it's whistling, it immediately stops.
- The whistling is louder if the A/C is running.
- The sound is coming from outside of the car and isn't an under-dash air
leak.  You can't really hear the whistle unless a window is open.
- This can't be duplicated either by revving in neutral or in gear with your
foot on the brake, the car must be moving.

TIA for any help.