From what it appears he used a bread tie end to poke into the airflow hole/s to clear it of debris. Granted I can see this is for the Phobia RDA.
In general principle though it
ought to work for
most RDAs. Barring that I might want to check wick placement, ensure you've not gotten wick into an airflow hole or passage.
Sometimes though you may need to tool on the outer cap of the RDA, bore the outer influx hole/s out just a bit bigger than the inner holes. You may have a piece that got a dimple which causes the whistling. A lot of the NaRDA styled RDA had this be the case. It was a simple fix once it was realized that is what the problem had been.
If it's not the external cap doing it, bore out the internal hole/s a bit. One way or the other
should give a fix. Not making any warranties or guarantees, only offering what has
seemed work anecdotally. Maybe it didn't work at all. The whistling though caused the users a psychotic break and delusion that it did. We could all be running around still whistling our fool heads off but don't notice and everyone is too polite to say. *chuckles* Never can tell. Now, let me check if reality is convex or concave this morning.
*pokes reality with a stick, runs*