In Moe DeLoughan
wrote:

You may have had a vehicle with a two-way radio running in the
vicinity but out of sight. A couple of years ago we had an Xcel truck
parked on the street for a few hours and we heard that. Didn't hear
any conversations, just the squelch or whatever they call it. Same
thing previously with an SPRWS truck parked at the end of the block.
That one was out of sight, prompting me to go out and hunt it down.


This makes more sense than anything I came up with (except the UFO).

It had been the first 90F day in a while and maybe Xcel was out hunting
down a transformer that was feeling the strain from everybody turning on
their AC at once.

If it happens again, I'll put on some shoes (and maybe some pants) and
take a look around.

--
St. Paul, MN