Getting back to the point, I agree that this is a harmonic of a cheap device which has a bluetooth transceiver in it to connect to the mobile phone, and a standard (albeit poorly filtered) FM broadcast transmitter in it, so you tune your car stereo to the frequency of the thing, and it's "pseudo bluetooth". They often plug in to the cigar lighter socket and have a small display on them. They're about $20 on eBay, Amazon, Etc.
I have one of these things in my agency car, and I'm very careful about what I talk about on it. I mostly use it to stream music to the vehicle which has no bluetooth. Many times I've had people pull up next to me when I'm listening to legitimate broadcast FM (I am one of the oldies that actually still does that), and their device is on the same frequency of whatever station I happen to be listening. I hear their music, their phone calls, etc. clear as day, it totally wipes out the broadcast station. For as small as these things are, and the essentially nonexistent antenna they have, they are unusually loud.
These things probably run an excessive amount of power, have little to no harmonic filtering, and that is unquestionably what you're hearing.
87.7MHz *3 = 263.100MHz
88.5MHz * 3 = 265.500MHz
etc. etc. etc.
And it's WBFM. Because that's what FM broadcast is, and that's what the car stereo expects to hear. Next time it happens, divide the frequency you're hearing it on by three, and go listen there. If there's no overriding broadcast station, you'll hear the same traffic.
Since broadcast transmitters (nearly always) have SERIOUS harmonic filtering on them, that's why you don't hear the third harmonic of them.