2003 Ford F-150 vibration

I have (2) problems for which local mechanics cannot hear and tell me nothing is wrong. #1 pertains to a vibratiion/rattle which occurs @ 25-30 mph. You cannot hear this with the window down, & the passneger cannot hear it, but it is obviously there and quite noticeable @ 28mph. Could this be in the exhaust system? #2 is a definite whinning at 45mph. If you take your foot of the accelrator, it goes away. Sounds like it is coming from rear axle area.