I don't really listen for a whistle(it's there though). I watch for the vapors coming on and know how long I can leave the flame on with out scorching, this just comes with practice. If you have a larger flame with out the ability to lower it then inhale really fast just like it says to do on the website. Small or large flames work equally well you just adjust you air speed to it. If I slow down my inhale on a medium to large flame it'll heat up so much I'll scorch the herb.

Mine in reality is really easy to use and I hardly ever scorch, I have ground up herb in my bowl and I'm geting vapors in 8 seconds of the first hit, hits 1,2 and 3 are very nice then I stir every 2 hit for 6 more hits for a total of 9-10 hits. I have ZERO problems geting vapors. You need to realize that vapor are only .33 as thick as smoke.

No Vapors to me seems like low heat and not enough herb the bowl, it should be halfway full of GROUND herbs.