Need to be careful as I believe there is true Encryption which may have a flag in the data stream and the scanner should not open the squelch, then there is Scrambling which is not Encryption and may not have a specific flag in the data stream and the scanner may open the squelch and you will hear the digital blurps as mentioned.
Scrambling is a much lower level of privacy that usually uses a voice slicing technique and if you listen carefully you can understands parts of the transmission, but it is kind of like "Pig Latin" where the voice is chopped and mixed up. Might sound a bit like SSB when monitored using an AM demodulator.
Scrambling is usually a feature set of some P25 systems and may be at no or little cost and is much easier to manage. It may also allow users to enable Scrambling on an add needed basis when talking peer to peer. So sometimes you may pick up intermittent Scrambling for a single talk group or a specific user group.
Encryption typically is a higher cost option that requires quite a bit of system management and thought to implement. Key management becomes an important issue as well. More often then not there is more money required so you will no usually have systems go to Encryption without a lot of thought both administratively and financially.