I thought the rear end of my 2012 GT
A6 was making more noise than it should. It was not "singing", just noisy. More of a slight roar. Service rep. went for a ride and agreed that it would be fixed under warranty. First gear set and bearings came in and were installed. No good. Gears were cut wrong. Hopefully the replacement set will be here Monday.
Service rep. is an old hot rodder like myself. The vent was bad also.
You would think the folks at the Ford Sterling Axle Plant would get it right. I had a gear whine in my 2013 F150 that took three tries to fix.