I'm trying to discern the difference between a pinion bearing whine and a driveshaft bearing whine on the rear axle of my wife's '91 Cherokee.
The whine comes/goes with different throttle application, worse at 20-45 mph, almost disappears at 50+. Does not change with direction of travel. (Normally, I hear an axle bearing get louder/softer when turning, but go away or get worse when straight.) The sound is much like running extremely knobby tires on the street.
She says it has made this noise since she bought it used 3 years ago. The pinion seal area is slightly wet with lubricant, as is the left-side of the axle housing. Lubricant level is normal, and when checked looks fine - no burning or off-odor, which *probably* means that the ring and pinion are OK. Wiggling the pinion yoke yields no give at all - solid as a rock. All U-joints feel OK, however there is some slop at the transfer case output case shaft.
I plan to have it looked at in a few weeks, but I'd like to be armed with some information before the mechanic starts checking my credit score.
Is it possible that the slop in the transfer case rear output shaft could sound like a bad rear differential bearing?
What say you?