I am hearing a "howl" inside of my 02 F150 when driving. At 75-80 mph it gets really loud. Is it a rear end problem, old tires (currently 4 yrs old) or something else?

 

it could be anything, really, but you've got two great places to start there. i personally believe tires have a max life span of 5 years, so you're getting close to replacement time there. rear end noises can be an expensive fix. if you believe that's the case, i would just deal w/ it for as long as possible, unless you can fix it yourself.