A while back I posted something here about a noise coming from my 03 4Runner (115K)that I thought could be a bearing on the way out. I got some useful background info here and then took it to my usual mechanic. My mechanic heard the sound (most audible when coasting between 35 and 40 mph)but couldn’t find anything wrong. He said he had the thing up on the lift and checked the wheels. No sound; no looseness. For good measure, he changed the rear diff fluid and rotated the tires. (The tires are in good shape and have about 20K on them.) Normally I would just crank the tunes and drive it, but I will soon be taking a 1500 mile trip with the family. So, should I get a second opinion? If so, where else might I suggest that a mechanic look, in addition to rechecking the other mechanic’s work?
Talk to everyone you know and find out where they take their cars for repairs. You will probably find a couple of garages that several people like. Call them and describe the problem, and ask if they will check it out for you. As a new customer, they may charge you for the diagnosis. If so, ask if they will credit a part of the diagnosis to the repair if they find the problem.
Your 4 Runner has all kinds of parts that rotate, 2 drive shafts, 4 axle shafts some with CV joints, 4 wheel bearing, and of course it could be some brake part(s) rubbing on something.
If your mechanic checked out all the possible items that could be major problems, that may be the best you can do. Another mechanic might find something, or might come up blank too. You can start replacing all kinds of parts, but that is going to get expensive and may or may not take care of the noise.
Crank up the tunes and just enjoy the trip. 1,500 miles isn’t that long and you should be fine.