Makes sense. Yes, I've got a regular vehicle, no diesel. Its weird, I just was there today for a short time and the buzzing was not there even with my car on. Its just sporadic I guess. That's what I was thinking as well in regards to the "scruffy" transmissions. Some are quite clear and some aren't. I was perhaps thinking it might also have something to do with the pilots radio, but if that were the case, perhaps ATC would also hear the scruffiness I'd hear as well.