66hz? Odd.... maybe the chip tweaks out a bit at lower voltages... ANY of the 33hz chip'd mods can rattle.... the SVD and Vamo both have the same type of chip, hell it might be the exact same chip for all we know.
But, the rattlesnake seems to enjoy clearos... I think it's due to that tiny coil in there. I would hear it rattle when I vaped Evods, but since I've gone to RDAs and RBAs, I've yet to hear it. I think what is going on is that those tiny coils in the clearos are basically NR-R-NR wires with really high gauge/resistance wire for the actual coil. That wire heats up, and cools down, lightning fast.
The bigger, lower resistance wires in things like your RSST, or my RDAs, they smooth out the pulses since the temp of the coil reacts a lot slower to the applied power.
I bet if you had some fancy, schmancy, super small thermocouples that you could attach to the coils, with the small coils in those clearos, you would see a sharp, 33hz saw-tooth as the temperature rises when it's fired. But on that monster 10 wrap 28g microcoil I have in my IGO, you might see a slight wobble in the graph, but it would be much smoother than the small coil. That's where the rattle, or lack thereof, is coming from... pressure impulses of vaporization coming from the uneven firing... and some devices amplify the sound due to their design.
At least that's how it makes the most sense in my mind.