RE: localised radio interference
Yes its possible that you are getting interferance.
Let me tell you about a funny source of interference that most people don't know. We had the same problem here in Texas. There was a spot. The spot was just off the end of the runway, so you were typically low and slow on approach when you encountered the glitch. Some months, the glitch was fairly severe and other times it seems to be gone.
It turns out that the oil comapnys actually find oil by looking for magnetic anomolies like this. Apparently the salt dome and oil are located in a large pocket that is essentially a dent in the earth. A thin spot in the mantle or crust. The earth is a big magnet. You can locate oil reserves by detecting these magnetic fields over oil domes.
So, besides man made interference from microwave towers and such, there are actually natural sources. The effect is much worse if you are flying AM radios, but I have experienced it with the newer FM radios as well. Its generally close the the ground. If you were quite high at the time, then this probably wasn't the cause.