Whine (when in reverse) after synthetic fluid change

[nscarnati]

I changed some of my fluids about a month ago to synthetic, and since then, I've been noticing a whine when going slow in reverse

- Rear diff -> Royal Purple Synthetic
- Transfer Case -> Mobil 1 Synthetic ATF
- Oil -> Mobil 1 Synthetic

The Royal Purple said it had a friction modifier in it, so I didn't add any to the rear differential when changing it. After dealing with the whine for the last month (noticed mostly when backing into parking spaces), I decided to add a friction modifier to the rear differential this past weekend. I've driven it now about 400 miles, and I still get a whine (which i think is coming from the rear differential) when backing into parking spaces.

Any idea what's causing the whine (if its not still the rear diff)?

 

[nscarnati]

anyone got any ideas??

could it posibly be the transmission (and just co-incidentally happened at the same time I was changing my diff fluid)? I don't hear a whine in 1st gear though, just in reverse going slow