2013 CRV - Loud road noise after differential fluid change

Hello - In January of this year, my 2013 Honda cr-v oil change, differential fluid & tire rotation reminders came on. I took my car to my local Honda dealer where they changed the differential fluid, oil and rotated the tires. Immediately after leaving the dealership, the tires handled much differently and there was a substantial amount of additional road noise (mostly coming from the rear of the car). I chalked this up to the rotation of the tires and the fact that several months earlier we had completed an approx. 3500 mile road trip. (Tires had never been rotated since purchasing the car)
I eventually became used to the noise until I started to get a vibration at 35 mph and then anything over 65-70 mph. We pulled the tires off the car this past weekend and decided that the noise and vibration was likely coming from my tires. I ordered 4 new ones and had them installed today. The vibration is gone however, the road noise is still coming from the back of the car. I'm not sure how to describe the noise other than a constant, growl from the rear of the car. Could it be possible that the dealership did not fill up my differential fluid enough, etc.? Other possibilities?