Noise from rear of truck.

[Weggie4]

I have a 2019 ram bighorn, crew cab, 6/4 bed. I have a whistling noise from rear end 40 mph and above. Noise does not change with speed or RPM. I put the rear end on jack stands so to rule out wind noise. Did research found recall U88, I checked my rear axle fluid almost 3/4 low,that was to first knuckle. It has been to dealership they replaced pinion gears, seals and bearings. Still haven’t taken care of the whistle. It has been there for 9 weeks. They want me to pick it up until it is a bigger issue.
Has anyone had a similar issue?
Any ideas?
Thank you.

 

[Weggie4]

Update:

came off the factory line with wrong shims in the rear end.

 

[Billy James]

I have a 2019 ram bighorn, crew cab, 6/4 bed. I have a whistling noise from rear end 40 mph and above. Noise does not change with speed or RPM. I put the rear end on jack stands so to rule out wind noise. Did research found recall U88, I checked my rear axle fluid almost 3/4 low,that was to first knuckle. It has been to dealership they replaced pinion gears, seals and bearings. Still haven’t taken care of the whistle. It has been there for 9 weeks. They want me to pick it up until it is a bigger issue.
Has anyone had a similar issue?
Any ideas?
Thank you.

U88 says its for the DS (4th Gen/Classic). Do you have a DS (Classic) or DT (New Ram)?