Still trying to get a low power rocket to whistle. Still failing. This is a 4 split fin rocket (so technically 8 fins, 4 splits.) Splits vary from 1/8 to 1/2 inch. The fins are papered and square edges (no rounding or air foiling.) Also drilled a bunch of holes from 1/8 to 1/2 inch. Hope was that the intentional messed up air flow would cause a whistle. Used a QuestJet D motor. Still no luck. I am thinking that whistling in rockets may be more serendipity than planning. Again, the pink tape strip seen on the nose cone is my preloaded configuration. I sometimes prepare my rockets for launch including wadding and chute prior to transport. To keep the nose cone from falling off and undoing all or part of my work, I put masking tape on to keep the nose in place. After an embarrassing lawn dart (actually Playa Dart at NSL last year) when I FORGOT to take the tape off (even Estes ShotGun ejection charges don't overpower a taped on nose cone!) I got some pink tape that is VERY OBVIOUS (especially when you intentionally leave a strip hanging out in the breeze) and less likely to launch the rocket in the (too) securely packed configuration.