There is an odd hum coming from the rear of my '99 expedition xlt. If I'm driving it for more than 15min it will just suddenly start to hum. Is there anyone out there that can tell me about this? Any insight would be greatly appreciated. Thanks.

 

Never heard of it. Maybe rear diff. once it gets warmed up?

What rear suspension does it have? Load Leveling air or not?

 

Don't know if this helps, but my wife's Explorer just went through a set of carrier bearings in rear end @ 43K. Had severe pitting and close to a real problem.

 

I've noticed the same type of "hum" in the rear end of mine ('98 with non-air susp./ 56,000 miles) in the last month or so, also.

 

Fuel pump?
Does it do it with the truck started and in park or only when moving?
If it does it when not moving, try this. With the truck shut off and in park turn the key to the on position without cranking the starter. The fuel pump will come on until the fuel system comes up to pressure and then shut off. I have had some Ford fuel pumps get really noisy in the past. My 93 Grand Prix right now makes quite a hum.

 

You sure Bill Clinton and Monica Lewinksi arent back there?