@JoeBearcat
The Play Button in Sentinel will NOT attempt to play the Audio.
If you are referring to the screenshot you posted before, there is nothing to play for Sentinel.
As an example, have a look to the frequency 468.925000 - there are 54 hits count with total of 31 seconds of audio. That means the average audio recording length for each hit is less than 0.6 second. So immediately after you press the PLAY button, the Sentinel just attempts to play this extremely short recording and stops after 600 milliseconds. And if you have the digital waiting time set to the default 400ms at the same time, that means there is no audio at all to play.
That makes things more interesting/complicated - there may be several reasons to this. Either the hit detected by Sentinel is a control channel as suggested by
@JoeBearcat, which means this is a Type-C trunking NXDN network (The Type-C NXDN trunking network use traditional control channel, which changes frequencies from time to time, that explains why you may have audio on the same frequency, when the control channel is switched to another frequency next day). It can however also be a Type-D NXDN trunking, which is a distributed architecture with no control channel - in such case, these hit may be some short data transmissions as suggested above.
Another reason could be encryption - I am not 100% sure about the Discovery function in sentinel, but during scan, it skips transmissions, which are encrypted - so his might also be the reason why you see recordings of several hundreds of milliseconds only
It is also possible, that the Discovery function is broken, however to be positive on this, you would have to verify the on-air audio with the use of another tool - best is DSD+ FalstLane, which provides a lot of information about the transmitted data and audio.
So I think your problem is not "why Sentinel doesn't play any audio?" as there is NO audio... the question should be "why Discovery doesn't record any audio?" - and the possible reasons are described above.
