So I've noticed something weird. I have the stock street tires on my 2011 f150 xlt 4x4 and it's very quiet on the road. Whenever I decelerate from 60 mph, I hear a subtle howl that seems to be coming from the rear end. It's like a gradual sound that sounds like gears whining down. Normal for this truck??? Now, my dealership installed a new flange on the rear end because the original was making a knock and shudder on take off. The tech said the flange also had an oil slinger in it that went inside the diff. Wondering if that's what is causing the noise?