This one has been a recurring mystery every summer for at least the past three years, maybe four or five. Need to look up past logs if I still have 'em. It generally shows up a bit excessively strong at first, then backs down to a more typical/honest signal level, and disappears in late summer or fall.
Another anonymous one to watch for that maintains a similar intermittent summer-only schedule is PLM, which was seen around 13557.75 last year.