Thought I was nuts . . .
Same thing happened to me not long ago while using my PSR-600. I kept hearing law enforcement traffic in the upper 700 MHz range but I knew there was no one within at least 250 miles using this band. After listening for a while I was able to determine it was one of the bordering county sheriff's office agency's dispatch channels, as I could switch back and forth from where I was hearing them on 700 MHz and their actual trunked channel, which is a Motorola Type II P25 system utilizing the rebanded 800 MHz set.
I thought I was going crazy though. Turns out it was just the scanner playing tricks. Whew . . .
Randy