2002 Toyota 4 Runner whining noise in drive shaft area

when driving a steady speed, say 40mph, lightly press on the gas pedal and then let off, just enough to change speed a few miles per hour. If the noise changes pitch, you have a pinion bearing problem. If the noise doesn't change, then you have a lot more things to check. I am assuming they checked to make sure the fluids where full for the diff and transfer case right?

Thank for responding. They did check the fluids and they were normal. The sound does change pitch. I have been searching pinion bearing issues online. I came across a YouTube video of a guy driving in his jeep with a bad pinion bearing. My issue sounds just like that. (I made a video but not sure how to post to this thread. No link on my iPhone) I also saw another site where a test for a worn pinion bearing was that there would be play in the joint where the drive shaft meets the rear differential. "Here's what you do.....place in neutral. Crawl under and shake rear driveshaft while observing pinion yoke....any slight movement indicates a loose pinion nut and/or worn bearing." I tried this (in park) and did not feel any play. Is this still likely the pinion bearing?

A stethoscope on the differential housing at the pinion area will reveal that very quickly and easily. Pinion bearings are pre-loaded and should have a specific amount of torque required to turn them. Easy to hear and find in the air with a stethoscope. I would hope that they intended to do a lot more than just pull a drive shaft for $160! I'll bet you have bearings failing in the transfer case.

You won't feel play in the bearings, typically the bearings or bearing race simply get little pits in the metal and the bearing make noise when rotating across the pits. I would have the rear diff fluid drained and refilled, the diff has a plug at the bottom to drain the fluid out, very easy, and inspect the old fluid for any metal flakes, if it looks like it has "glitter" in it, or some silver tint, you have found your problem. on the other hand, I have never heard of a Toyota diff have any pinion bearing problems??

Had the truck at the shop today. They dropped the axle and determined the noise was from the xfer case. I have never had the xfer case oil changed (didnt know I had to change it) so we decided to change it. The old oil was very thin compared to the new oil. The noise is still there but not as noticable. Hopefully I have not damaged the xfer case too bad and it won't have to be replaced. What are the signs that I should be looking for that will tell me that the xfer case needs to be replaced and failure is imminate.

Unfortunately, if the xcase is still making noise after fluid change, failure is imminent, the case has bearing just like the diff, and one is probably going bad. The noise will get louder and louder, and eventually something inside will have to much play and will either seize up, lock up (my dads jeep wrangler xcase locked solid while on the highway and locked up the rear tires causing him to lose control and end up in the ditch) or you will hear a lot more noise than just the whine, like crunching or grinding. Either way, start saving :(

02 4runner sr5 4wd I'm having the same problem but i set my truck on jack stands and the noise is coming from the drive shaft i was told i hit something while going for it off road and bent it but i don't recall doing so. I'm changing it out soon for a used drive line. my current one is pretty rusted