Pro-85 problem

[Boosch101]

I have a Pro-85 scanner and it works great. Except for this one situation that I encounter. When I pick up a frequency of a nearby security guard I can hear him speak sometimes but not every time. Also when his base responds to him I only hear static on the same frequency. Are they using some type of encryption or is it a digital signal that I cant pick up on my Pro-85. How can I solve this problem.