Handgunner,
My own belief is that it probably makes no difference whether or not you yip or bark a time or two before the howl. Generally my first howl will be a howl only followed by a few seconds of silence, then a couple of barks and a howl followed by a second or two of silence, then another howl. Coyotes do their howls both ways, so it probably don't matter much. I just like to mix it up a little. That is just me I guess.