Thanks! My favorite station is Hawaii Public Radio (call sign KHPR)
at 88.1 MHz. I couldn't identify the other station. It was so noisy
and it was gone soon after I noticed its existence.

I don't know how close you are to your neighbors.
But iPods and other audio devices now feature FM transmitters to play on
your home or car stereo.
It could be a neighbor was setting theirs up and didn't realize it defaulted
to 88.1 at the bottom of the band.