Your right about the distinct sound of the Huey, no other helicopter sounds like a huey. For those that aren't aware that distinct sound comes from the advancing rotor breaking the sound barrier. To this day I can tell what kind of helicopter is coming just by the sound it is making. The 540 rotor system on the C-Model and the Cobra are considerable louder than that on the slick and could be heard coming for miles. Its was hard to sneak up on "Charlie" when your coming at him in a Cobra at 140 knots but just as well I liked let him to know what was about to decend upon his behind.
Have a very Merry Christmas.