I have had a good bid of success with using a CD call i downloaded from the internet. You could hear this guy breathing and everything on the Cd, But it works! I have called in lots of coyotes with it , in my truck CD player/I usually just back the truck up into a patch of mesaquites and open the doors, disable the lights and door dinger thingy ( i hate it) But i play the cd player really loud, as loud as i can get it. I actually have to use earplugs when i hunt because the call is so loud try this link. it is where i got the audio for my calls
http://www.varmintal.com/ahunt.htm