It happens even when I'm alone with the radio off. Ha-Ha. I have a set of Mechanics Ears ( bunch of sensors that feedback to a headphone) I'll try putting that on the car on the front diff, next to the brakes, and on the front of the engine and see if I can isolate where the noise is coming from. I'll post the results if my wife will let me continue on a website which allows sexist remarks - seriously guys think about your comments and decide if you might be a little sexist) I know that the beginning of my previous sentence was sexist and demeaning to women and I put it there just to make a point.
