The Sharx and Sonik Blast are like the older Classic, except the newer Fox40 whistles are a bit louder.

The Storm does have that oscillation and is a heck of a whistle. The oscillation in frequency is due to the pea rattling around in the chamber, thus causing slight frequency changes. What you hear may actually be oscillations of loudness. I don't know what is technically correct here. Note that any pealess whistle, like a plastic Fox40, is NOT going to have that oscillation sound.

A finer point...The Storm provides better control on loudness. I think that's due to the pea. That control may or may not be useful to you. The Fox40 kind of goes from soft to loud, with not much in between. I personally have a whistle for emergencies, NOT for dog training or normal communication or whatever. So, control is not really all that important to me.

By the way, I've developed a slight obsession with whistles over the last month. The technology and the histories of the whistle companies have fascinated me. Also, a whistle probably has the highest value/weight ratio of anything in your survival pack. An example of a probable survival situation for me is an earthquake that causes me to be trapped in a structure, like what happened recently with people in Haiti and Chile. So, now, I just wear a whistle all the time like a necklace.

Oh, I plug my ears now, but I had to experience the full loudness once for each whistle because I was curious.