Greetings and salutations to the Toyota fan club! We've got a 2004 Highlander AWD with which we've been pretty pleased over all, and I'd like to keep if even after our lease is up; but it has a really annoying quirk which no one has been able to eliminate. The factory tires (Toyos) were junk: slid all over the place in the cold weather even though they were brand new. In wet weather, even new, the tires made a wa-wa sound between about 20-40 mph; at about 12K miles they started to make the sound even on dry pavement. At 15K the sound was always there even though the tires had been rotated as per the book (I'd never heard of a 5000 mile tire rotation: that's ridiculous!). I couldn't stand it any more and put on new sneakers at 18,600 miles. High speed balance, wheel alignment check (AOK), everything is tight and according to spec. Exactly the same thing happened with the new tires, and in the same time frame, too. I had a 4-wheel alignment done at a different shop (the third one involved) and they told me that there was barely any adjustment to be made, but they made it. Everything is ship-shape, but it's not hunky-dory because it (the wa-wa-wa-wa) continually gets worse.
Does any body have an idea or a solution? The Toyota garage doesn't even count: they heard the sound, but they don't see a problem. Course not: they don't have to live with it. I know--I'll turn up the radio!
Any suggested diagnoses will be appreciated.

old post...but yu never stated what kind of new tires yu did put on.

As you can tell, I gave up with frequent visits and I just log on whenever I feel like it.
Old response to old post:
The original tires were Toyos, a highway tread which the dealer called "all season," but they were more like
"dry weather, asphalt only." I don't remember the design name. The replacements are Cooper
Discoverer ATRs, and they are GOOD tires. I have had no winter-weather problems at all with them,
unlike with the Toyos (I live in Northern NH, by the way). I experienced no change in fuel economy, either,
so I've left them on all year long, and they now have about 33,000 miles on them...well, on three of them:
one acquired a cut in the sidewall at around 20K.
The sound that I complained about is still there, as it has been since the car was new, and no one has
suggested a solution or a cause. The tires have been rotated every 5K with the exception of a trip to
California and back in which case they rolled on for 10K.
My lease is up next July; were it not for the wa-wa I would gladly keep the car, but since it has annoyed
the tar out of me for four years already, it will be up for grabs.