Cadillac CTS-V - Bad rear diff howl

2005 CTS-V with 90k miles. Terrible loud howl at highway speed coming from the rear. I hear it basically anywhere above 50 mph. It will still howl at 50+ mph when in neutral. There are no leaks that I could find after getting under the car and checking the rear out. The diff fluid hasn't been changed in probably 25k miles so a fluid change with maybe LSD additive would help?
What other tests can I do to nail down the root cause?
Is it possible that the rear is on its way out?

All the rears in these cars whine. Try to find a 4th gen diff from a 07. It'll still whine but with my experience won't grenade.. I've been down that road twice

My 4th gen diff whines significantly louder then my first gen ever did :(

If it's just noticeably noisy it's probably OK, if it's screaming loud, then something's wrong. Change your fluid and put some heat wrap around the adjacent exhaust pipes. I've found that the hotter they get, the noisier. I barely notice my whine anymore with it heat wrapped.

If it has recently became louder, there is something wrong. Check your fluid for metal. Could also be called glitter or bling. Sorry, couldn't resist.:(

The 4tH Gen I had in my car did not whine at all.

I didn't notice it until I put the cs diff bushing and block. Its heat related as it takes about 15mins to get it to speak up.

My 04 original diff is silent until 83 mph. Only then can I hear a slight whine with the back seat down. Other than that, she is solid.

Definitely change the fluid and add additive. Some go with a heavier weight gear oil to quiet it down also.

Thanks guys. The car does have an 07 rear in it. I will try a fluid change. If i didnt know any better, sometimes i hear the whine and sometimes i dont. Maybe ive lost my mind lol!!! Will keep everyone posted