So all of a sudden this morning, I started hearing this sound like a hum, like an propeller aircraft or one of those little cars with the huge mufflers, and it rose and fell in pitch with the speed of the tires (NOT the RPMs of the engine). At first I thought it was on the left rear, now I am thinking it is on the right. I checked the tires to make sure nothing was stuck in the tread, and couldn't see anything. I am going to take it into the dealership tomorrow as we suspect it is something mechanical like a wheel bearing or something with the AWD mechanism. I have over 12K miles on the car at this point.

I will update as I find out more.

 

One case has been documented in this forum, months ago, about the Active Noise Cancellation acting weird and sounding pretty much as you described. I believe there is a setting, from the screen menus (in diagnostic mode?) where you can turn off ANC? Could be the same here?

 

I took a quick drive with the tecnician and we had gone maybe 100 yards when he said, that's a wheel bearing. He was surprised because this is obviously a relatively new car (got it in Nov 2014). He thought it could be either the left or right rear or both (my suspicion is both based on the way the sound has shifted from LR to RR and back). They didn't even have the parts in stock so won't get the car back until tomorrow. Plus it turns out there was a recall about the transmission slipping into neutral, I have never had that happen but maybe it will provide yet a further refinement of the 2-3 shift. :-)

 

The left rear wheel bearing went out on my tlx also! Had 6300 miles...

 

wow only 6300 miles and a bad bearing .. that's pretty strange