I have a humming noise and very minor vibration that comes and goes at speeds of @ 40, 60, and most pronounce @ 73 mph. Also continues to come and go at higher speeds as well. I had an electronic vibration analysis preformed which picked up the vibration @ 108 Hz. and but could not pin point where it's coming from. Sounds like coming from the front but hard to confirm. New PSS recently installed and load balanced. Wheel bearings inspected with no issues. Noise is there with/without car in gear or coasting in neutral. I have a DSS one piece alum. drive shaft installed but noise was there prior to install. My thought is rear diff. as I blew a right rear axle seal during a track day and leaked a fair amount of fluid. But humming noise doesn't sound like is coming from the rear and vibration I can feel in the floorboard but very minor almost more like a tingling. I'm out of ideas and my local Ford dealer has also not been able to track it down. I've now run three track days with this issue and at some point I'm afraid of some type of failure. Any ideas????