While in St Louis a few years ago I heard these same beeps/tones keying up repeater's in that area. The next day while in Oklahoma I heard the same beeps/tones keying up repeater's in that state. Then, the next day after that while in Texas I heard the same beeps/tones keying up repeater's in that state.
All connected, all with the same beep's/tones, ALL happening right about the same time of day. At the end of each beep/tone, there was a loud burst kinda like DES but it was not DES. Sounded more like a break in squelch but DEFINATELY not any form of encryption.
Also, recently while in the mid-west I heard on 167.7125/analog, P-25 ENC trying to pass through that repeater. The signal was fairly strong and you could hear the P-25 trying to pass through but completely un-readable due to both being different forms of technology. Then after that a unit tried calling on the analog side but the response was trying P-25 ENC.
This was just an experience about 2 yrs ago. Now, I just hear the repeater keying up but no beeps/tones or loud burst.
I am no expert but this is my two-cents and maybe it helps. Happy Scanning!