TSA Encryption

I've started noticing some changes in the TSA communications in my area and wondering if the same is happening in other areas as well.

Until recently, all of the TSA P-25 communications at my home airport of Portland, Oregon (KPDX) have been unencrypted. Simplex communications at all the security checkpoints has been on 172.1500 MHz, with different NAC's for each, and some administrative type communications have been heard on a repeater on 172.9000 MHz, N001 (169.3000 MHz input). About three weeks ago, I started hearing a lot more activity on the 172.9000 MHz repeater, but it was all encrypted. Until that time, I was only catching some random, brief encrypted traffic when someone accidentaly switched the secure mode on.

With some exceptions, most TSA traffic seems to be in the clear. San Diego has been encypted for quite a while now, and perhaps others.

While I'm not sure if this might be related, but I recently spotted some marked TSA vehicles that indicate they are operating more than just baggage screening and passenger checkpoints. The new-looking trucks were marked "EXPLOSIVE DETECTION K-9 TEAM", and were parked on the ramp area of a major aiport. Could these secure communications be tied into more activity by TSA activity not normally seen by the public?