New (to me) CX-9 with oscillating vibration.... help me diagnose?

I bought a 2009 CX-9 with 63k last week to replace an aging Jeep Liberty. This is the third Mazda for our family and we have been very happy thus far. (I still drive a 1990 Miata to/from work in the summer). In one week I have: Changed transfer case oil to royal purple, ordered a Reese hitch, roof cross-bars, and a new key.

One week in:
I am very pleased with the size and drivability. However I've now noticed a sound/vibration that wasn't apparent on the test drive. I've searched a bunch and this forum really has the best cx-9 community out there. Maybe someone can help with this one:

The car:
2009 CX-9 Touring. 63k miles. New tires 4k miles ago with no apparent uneven wear. Had the recall control arms replaced earlier this year. Clean carfax, excellent body and interior looks well taken care of, but otherwise unknown history.

The problem:
-Vibration/dull roaring noise.
-Vehicle speed specific, but not at wheel speed: It is an oscillating on/off "Whaaa...Whaaa...Whaaa..." at maybe 1-2Hz when at 65mph, but does change with vehicle speed. Math nerds would say it sounds "sinusoidal". Shifting to neutral at speed does not change the noise.
-Only heard at highway speed above 50mph.
-Felt most in seat/floor. Not felt in steering wheel or when braking.
-Varies with slight steering turns at highway speed (e.g. changing lanes or gentle curved freeway turn): Worse turning right, better or absent entirely turning left. Note 'turning' is used loosely as this is only slight steering input at speed.
-Slow-speed circles on a smooth parking lot show no sounds/catching/abnormalities going hard right or left. Cannot hear noise at surface street speeds.

The Work-up:
-I got under the car (need to find a higher capacity jack for this beast) and the tie rod ends were shot. Still together, but maybe 3/8" of play on each end. The '3 and 9 o'clock tire shake' showed maybe an inch+ of play at the tire! I immediately replaced both ends. Alignment was pretty good after, but I made fine adjustments with a string box and toe plates. Ive never done alignment before, but it came out pretty well: tracks straight and wheel is centered. Steering is noticeably tighter! The noise/vibration has decreased in intensity/volume by at least half, but is still there.
-Other checks showed tight control arms, no play in front axels, intact cv boots, no noticable play in 3-piece driveshaft or carrier bearings.
-I aired all tires evenly and torqued lugs to 90.


The Thoughts:
-This seems to me like fallout from some sort of curb-strike accident. Both tie rod ends AND some other component damaged?
-The oscillating nature has me stumped. Because it changes with steering I'd say front bearing BUT, it is only with slight turns at highway speed. I've had bearings fail before and they were more of a constant roar at any speed.
-Because it is only at speed I wonder if it is tire/alignment issues. I think I'm going to have a roadforce balance and at the same time see if the wheels are true. Could a bent wheel account for the noise and bad tie-rods? Wouldn't I feel that in the steering?
-Ive really ruled out brake/rotor noise or any driveshaft noise- unless someone thinks otherwise.
-Could this be the transfer case going or would it blow all at once? The oil was of course black, but not terrible: though I think I put more in than what came out.

Any ideas on what the next step should be? My gut says bearings, but I hate just throwing parts at a problem without understanding it.

My gut says cupped tires due to driving around for too long on worn suspensions bits and a bad alignment.

Run you palm along the tread in both directions and see if feels like little ramps catching you hand in one direction or the other.

This is a pretty good picture of what you're looking for:

The fact that you're hearing a very low frequency drone, combined with the fact that it's worse turning one way and better turning the other way, tell me that it's probably what's known in vibration circles as 'beating'. You have similar frequency noise coming from a tire on either side, but they're slightly different in frequency - what you're hearing is the signals alternately reinforcing each other, then cancelling each other out.

It might be a wear issue like eskimo suggested, but if your tires aren't too worn, you may be able to fix it with a one-side air pressure adjustment.

Sounds like the issue my CX9 had when i bought it. I assumed it was a wheel bearing issue at first, But Mazda assumed it was a transfer care issue, and replaced that. Probably continued unchanged until they figured out it was actually something in my rear end. They diagnosed it by actually removing my rear drive shaft, and driving it. At which case the sound stopped. Mazda ended up replacing my entire rear end under warranty.