I posted this on the F150 forum, but this might not be a bad place to start.
Picked up my 2009 F150 about 10 miles into a drive started hearing a loud vibrating/whirring noise coming from in the truck in the interior dash board area. Happens at 45 mph and also 60. Sometimes in between those speeds. I have a factory installed chrome bug deflector and tow mirrors. Both of those items are secure not loose. anyone else ever have anything similar. A trip to the dealer, didn't get in....they suggested the bug shield. I made sure it was secure...any thoughts?

 

I was wondering if you ever resolved your problem with the rattle in the dash? I have a 2006 supercrew that has a similar rattle that begins around 60 mph. Mine is on the driver's side and sounds alot like a piece of plastic bouncing around on a sheet of metal. Took mine to dealer 10 times. All that they said they did was pack more insulation in the dash. Still no change.

 

To:etexmedic, my vibration was the Ford factory chrome bug deflector. It was real noisy the whole length on the dash. Once it was removed-silence. When hunting for the source of the noise, I did look up under the dash behind the steering wheel, couldn't believe all the space Ford left blank. I could see sky thru the vin number space. Hope your noise is only the bug shield. Good luck!