Yeah, I noticed that too, but only when I'm listening to AM. Don't laugh at me cuz I listen to AM. There's only one AM station I listen to and you'd know what I'm talking about if you're way too into sports
What I've noticed also is that if I turn the volum all the way down, sometime, I'll get a buzzing noise coming from the stereo. I've never seen that before, but I guess it's another of those Honda/Pilot quirks.
Surrounding power company high tension transmission lines are very strong magnetic and electric fields that can easily distort or overpower your local AM broadcast signal to your radio receiver. The AM broadcast band is more suseptable than the FM broadcast band because of the type of signal and because its closer in frequency to the fields generated by the transmission lines.
Unfortunately Honda put a compromise radio antenna in the rear window which makes it easier for the fileds to interfere. While the window antenna is effective, its just not very efficient, so weaker signals on the AM band are easily overwhelmed by strong external noises.
The local traffic station has the maximum power the FCC allows - a clear channel station. Even with that many watts, power lines cause extreme hum. I wonder why Honda didn't use an antenna like the German guys use (could it be a cost driven decision???)?