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.