I live in Westminster and starting every August I hear three distinct night-time insects: cicadas (infrequently), katydids (constantly), and an unidentified bug that emits short (3-4 seconds) bursts of clicks. These occur about every 60 seconds or so, are usually higher in the trees, and appear to be calling/answering others about 100' away or so.
What in the heck are these guys? I can't get close enough to see them so I have no description for you.
Adams County Colorado insect issues
I bet it is the broadwinged katydid. they click and the time of year is right.
A sheet on this is at: http://bspm.agsci.colostate.edu/files/2013/03/Broadwinged-Katydid.pdf