Ive gotten a lot of good intel on coyote hunting on both Coyotegods.com and preditormasters.com I just bought a bunch of calls of the ones I bought the Dan Thompson PC1 Jack Rabbit is my favorite. Im still trying to figure out the Dan Thompson Red Desert Howler. The Verminator Tweety was highly recommended also and I picked up a Syco Tweety which has a split reed and makes the most intense shrill high pitch sounds you can imagine. I cant tell a lot of difference between the Cierce call's sound and the Dan Thompson PC1 but I like the shape and style of the Dan Thompson better.
You have to try and change it up alot, they maybe hearing alot of screaming rabbit, so start with challenge howl. Bucking the odds.com is a fun site too!