Folks:

I've got a 2003 V8 4WD 4Runner Ltd with about 75k miles on it. I'm getting a droning noise on the highway. It is a relatively low frequency noise that repeats several times per second. Sort of a wah-wah-wah-wah noise. It appears to be coming from the front of the truck.

I start hearing it around 55-60 mph and it increases in cycles as speed increases. I only hear it when driving at a steady speed, typically when the cruise control is engaged. If I back off the throttle, the noise goes away immediately, only to come back when I'm at a steady speed again.

It is not the tires -- I get the noise with both my summer Michelins and my winter Nokians. The dealer thinks it is coming from the air box, and checked with Toyota. According to the dealer, Toyota says that some 4Runners have this and it is normal.

I noticed this early on when I got the truck new, but it went away before I could get it back to the dealer. Now it is back and seems here to stay.

An independent mechanic thought it might be the rear diff, and he replaced the diff fluid. That made no difference. Any chance it could be the front diff? How would I diagnose this?

Does anyone know what might be causing this and how to fix it?

 

I think I solved the problem. I normally keep the roof rack cross rails all the way at the back. I had them moved forward to carry my surf rods.

I moved the cross rails to the rear and the noise went away. Weird. It really sounded like something that was rotating, given the rhythmic nature of the noise.

 

I've got a similar noise between 70-80 mph. Sure sounds like a wheel bearing to me, but it only occurs when I'm at part throttle. When I let off the gas it goes away.

I was advised on another forum to change my front diff/center diff fluid. I'll have my mechanic check the wheel bearings while he's in there....

 

I was having the same problem as paulunm. When i let off the throttle, the noise stopped. I sent my 03 to the dealer and they said my rear differential assembly needed to be replaced. They said it appeared to have been run w/ low diff. fluid. There were signs of rear pinion seal leakage. Fortunately my warranty is going to cover it. Should get it back any day now. Good Luck.

 

So I assume it was your rear diff? My sound definitely sounds like it's the front. Drivers side front wheel to be specific...

 

Yep, mine was the rear. You might want to grease the zerks on the driveshaft if you have a 4x4. Could be the universal joint. Other than than I don't know what it could be. Good Luck.