2004 4runner Sport, V6, 4WD, 110K miles, original owner

Need some help diagnosing a problem and deciding on a repair strategy. I'm getting a significant low pitched humming noise at highway speed that becomes noticeable at about 60mph. The noise is loudest in the front driver quadrant of the vehicle. The noise is accompanied by a light vibration that can be felt through the floor board. The hum tends to pulse over 1-2 seconds. The pulse tends to quicken when bearing to the right, and slow when bearing to the left (again at highway speeds only). There is no noticeable noise or vibration under 50mph.

I took it to the dealership for diagnosis of what I thought was likely a driver front wheel bearing. They road tested and put on a lift listening with a stethoscope. They did not detect any problems with the bearings. They checked the fluid in the differentials and found a "little bit of grit" (I have never had differential fluid changed). Their conclusion was the rear differential needed complete replacement for $2000, likely due to worn bearings. When I pressed them, they said they were only 60% sure this would fix my problem. They also said they had never had to replace a 4runner differential, and that they couldn't rule out the front differential.

So I'm obviously not going spend $2000 on a repair that is only 60% certain to fix my problem. The dealership said it would be more expensive labor-wise to tear apart the differential and diagnose/replace worn bearings/gears. The differential part is $1300 of the $2000 repair. I have not gotten a second opinion just yet, but I am considering it.

So I need everyone's experience and expertise to help decide on a course of action. Any thoughts on what the problem could be? If it is a differential problem, why is it loudest in front driver quadrant? And why does the pulsing hum change speeds when bearing left/right?

Thanks for the help. Any input is greatly appreciated!

Read this thread!!

Anyone changed there own front Wheel Bearings on a 4th gen yet???

I will guess it is a rear wheel bearing. Likely the drivers side. The sound can travel up the frame rails and fool you into thinking it is one of the fronts. Rear this thread and see if it helps.

Good Luck!!

it does sound like a wheel bearing.

I would get a second opinion. try an independent shop.

I would too get a second opinion. This could also be a tire problem. Have you eliminated the tires yet? As tires wear...they tend to get noisier (especially an AT type tire).