I think it may be Indian River or possibly Brevard county,not exactly sure which one..I would have assumed it was possible local interference however,I have the CTCSS Rx tone set and I'm not using CSQ for receive. I wouldn't think it would be possible for interference itself to generate a 156.7 PL tone to unmute the radio.
I heard this the other day when I expected one of those repeaters to be used during a hot pursuit, but it's gone now. I'm in eastern Broward County.
The problem sounded like a Spectra*TAC SQM that was chattering on the edge of decoding the guard tone from the remote receiver. This can happen when the either the decoder or encoder drift off 2175 Hz. If they're using a DigiTAC or other system then I have no idea how that works. But it sounds like it's time for some routine maintenance on that system.
What I don't understand is how it's keying up a whole string of repeaters when I have read repeatedly that they are only set up on request? Yet many times I've heard numerous repeaters heterodyning with each other when these random key-ups happen for long periods of time. I guess nobody at the control point looks at the status indicators unless there's a specific need.
It's like they forget they exist. A few days ago a neighboring county (Pasco) helicopter came into my county to look for a missing endangered subject, and a sergeant from my city (Clearwater) commented that they "probably won't be able to communicate with them on the radio." So there were three agencies, Pasco SO, Pinellas SO, and Clearwater PD on three different radio systems that all apparently forgot that there are 800Mhz analog interop frequencies available.