Front End Noise

I have a 1987 Dodge Caravan, 3.0 Liter v-6 with 118,000 original miles. I am the original owner. I have a problem with the front wheels making a rumbling noise (sometimes) when I approach an incline (5%) at 45mph or faster. If I let up on the gas pedal the noise would stop and when I depress the gas pedal the rumbling noise would resume. I have taken the vehicle to two mechanics who had the car tested on the highway and of course the front wheels did not make the rumbling noise. I noitice it does not happen when I am close to home, only when I’ve driven the vehicle for at least 2 hours or more on the highway. Any suggestions? Thanks!

Wheel bearings or the differential or the CV joints or something else. A good mech should be able to figure it out. Why don’t you drive for two hours and then take it to the mech to examine the car.