Ford Repair: Rear End Humming, ford ranger, rearend

Question
I have a 94 Ford Ranger with 260,000 km on it.  It runs fine and drives fine.  Lately it has developed a humming / whining noise coming from the rear end.  I do not notice it while driving, but it is noticeable while sitting and idling.  It started as a low noise, but is now getting louder.  It sounds like it is coming from the area around the middle of the rear axle. Any ideas?

Answer
If you don't hear the noise when moving then it's not the rearend. There are no parts moving in the differential when stopped. You probably have a fuel pump whining, one of the signs it is worn out and working hard. Or perhaps it is the muffler broken inside.

Many times the fuel filter is not changed regularly and the fuel pump is stressed by trying to push the fuel thru a clogged filter.