I had extended warranty. The dealer said he thought it was the electronic shaft to the rear wheels and replaced it at his cost. Warranty paid. $1600. Then replaced both rear wheel bearings. That stopped the growl but after it was gone I noticed a vibration like running on a rumble strip at 45 mph. Duplicated the vibration with the tech on board but no idea what it was. Warranty is out now but still have the rumble at 45. I think its there above but its hard to tell because of the noise from tires and can barely feel it on the floorboard yet.

Update from Jul 27, 2016: Toyota has extended the drive train warranty till 2017. Problem is no one can figure out what it is. I've had the tires rebalanced 4 times with no effect. It acts like a torque converter stutter, but, does it locked in any position 1st, 2nd, 3rd , 4th and 5th. I don't know if the lockup is controlled by recorded shift position or with a sensor that locks it without caring what gear its in and just on speed. It does seem like it started after toyota replaced the electronic rear wheel control box. $ 1700 unit. I'm dumbfounded. The rav has been a great car and I don't want to replace it, but, I'm concerned about taking it on a 1000 mile trip. I'm basically using it to go under 50 miles at a time.