Aw, the truck shouldn't have had that much of an effect.
Practic on your house cat or your dog, if you got'em. Blow low and slow, varying the tone and all by cupping your hand around the caller. See how they react.
When you're out calling, don't try to see what maximum db you can generate. Mostly start off a bit loud, but repetitive. Imagine a hurt rabbit, yelling loud and fast at first and then slowing down and not yelling as loud as he tires. Then, a 10- or 20-second pause and a sorta softer call...
Hey, what coyote's gonna tangle with a 400-pound rabbit?
, Art