I didn't notice this problem until I had my drivetrain replaced because of the 60 mph hum issue, but maybe it was there before. The issue occurs at or above 74 mph, but is most noticeable around 80 mph. It happens when you are right around zero energy usage on the energy meter. I notice it most often when coasting down a hill where the hill itself will maintain my speed of 80 mph while not using or regening any energy. I was told it was normal and have lived it with for a while, but then I got a loaner yesterday while I had a few minor things worked on and lo and behold the loaner has the same problem (and the loaner was a 32XXX VIN which is much newer than my 156XX VIN). Does everyone else have this same issue? It's not a huge deal, but it bugs me when I'm driving with the radio off and I go down a couple of specific hills that I hit every day on my commute.