Yeah, I was a little annoyed with myself when I figured it out - the signal bars were jumping around so it looked it was receiving something, otherwise I might have gone down that road sooner, but it fooled me into thinking the signal was still there but weaker. Must've been picking up some other distant system, or I noticed there's some sort of very regular data burst on another listed CC that doesn't sound like any trunking standard I've heard before, and maybe that's what it was hearing? Not sure.