UPDATE DEC.1, 2014: our demo unit of the BW Broadcast DSPXmini-FM SE audio processor arrived today. It's been installed on 88.1FM and initial tweaking is complete. The sound seems markedly improved. I'll be fiddling with it further to adjust it across different programs.
ORIGINAL ARTICLE: About a week ago, your intrepid engineer made some changes to the airchain on our 88.1FM that should've, in theory, been wholly beneficial and with no potential for downside. However, around that same time I started getting reports of an odd whistle...or just high-pitched static...that would come and go with no apparently rhyme or reason.
These reports aren't widespread, but there's been enough that I'm no longer inclined to think it's just an odd run of people happening to have poor reception. The only commonality is that it seems to occur only when reception of 88.1 isn't very good to begin with. Not necessarily "poor" reception at all, just not "super-solid".
We've talked in the past about skywave propagation, but it's cool when you heard about real-world examples of it. Recently I've gotten several emails from "DX'ers" (Distant Reception enthusiasts) in Europe saying they've been able to hear Latino Public Radio on 1290AM all the way across the Atlantic!
UPDATE 01/21: Multiple letters sent with no response, and the pirate's still broadcasting. A letter has been mailed to the FCC's Enforcement Bureau. If you are an RIPR listener to 102.7 and you have experienced interference due to this pirate, you can submit your own letter to the FCC as well.
UPDATE 12/19: The pirate has been found! Well, we're pretty sure we have found the pirate. Using a directional antenna and a signal meter, we triangulated the position to a house a few blocks from the Locust Grove Cemetery in South Providence.
A letter of notification of interference to RIPR was mailed to this address several weeks ago, but apparently this pirate doesn't care as there's still an illegal broadcast on 102.9 from this location.
UPDATE 11/5: Thanks to a fellow engineer who informed me there is a pirate broadcasting on 102.9FM and that is likely the source of the interference people have reported (see below). Quite possibly the atmospheric changes made it worse, but the bulk of the problem is likely the pirate.