2001 4-Runner

My 2001 4-Runner has 85.5K, has been well-cared for and is very clean. For a couple of years (at least) I’ve been hearing a light “wa-wa-wa-wa…” sound coming from the underside. I keep thinking it’s something to do with the drive shaft/u-joint because the “wa-wa” frequency is in direct proportion to the speed of the wheels turning. It’s there whether in gear or out (coasting,) whether in 4WD (high) and it hasn’t seemed to get louder over time. The only time it subsides or disappears is when I apply the brakes - that makes me think it might be a wheel bearing but the sound “seems” less centralized than the direction of one of the wheels.

I’ve had a reliable (to me) shop take a ride with me to listen to it and his advice was that I could spend more money looking for it than fixing it and to leave it alone unless the noise changed, got louder, etc. However, it’s hard to ignore it and I’m hesitant to go on a long road trip in it because of this problem.

Any thoughts on what this could be and/or whether I should pursue it or not would be appreciated.

It’s fairly easy – assuming this car is disc brakes all around – for a mechanic to do a quick visual inspection of all four wheel’s brake components, so that’s probably the first place to look for something obvious. Better if you can clue in the mechanic whether the noise is coming from the front or back, and left or right.

As part of this process of brake inspection, the mechanic can grab hold of each tire and wobble it right/left and up/down, see if there is any unusual amount of play in the bearing. Wa Wa sounds are often caused by wheel bearings on the fritz, esp on the non-driven wheels. If it gets worse when turning, that’s another clue for a wheel bearing. Turn left and it gets worse, then suspect the right side wheels. The driven wheels tend to make growling or roaring sounds.

If nothing in the brakes is obviously wrong, your mechanic is right that the least expensive way is probabably to wait until/if it gets worse. It’s sort of unusual to have wheel bearing problems at 88K. That usually happens at well over 100K, like 150K it wouldn’t be unusual. But hitting just one pothole at high speed can damage a wheel bearning, and if you are sure the sound is coming – say – from the back, and the brakes look ok, and there is some unusual play in one or both of those wheels, and it makes you nervous, consider to schedule to replace both back wheel bearings and be done with it. Wheel bearings are designed to be replaceable, so the bearing fee should be – pardon the pun – bearable.

Thanks, George. The “noise” is not identifiable as to coming from front or back. In fact, if I roll the windows down at @ 40 mph I don’t even hear it for the wind noise - that’s how slight it is. I’ll have the brakes checked - it doesn’t sound like any wheel bearing noise that I’ve ever heard but I can have that checked as well. It doesn’t change at all when turning right or left. It’s a real puzzle.